This page covers building the browser, debugging the browser, how we communicate and use Gitlab to organize our issues and development process, what goes into the browser itself, and also provides links to other development resources and information.

Ways to Build Tor Browser

The first thing you probably want to know is how to obtain the very latest (and sometimes greatest) Tor Browser builds, and how to build your own version of the Tor Browser from our source code. Well wait no further.

Nightly Builds

See this page for information about downloading nightly builds.

As with all of our builds, it should be possible to reproduce byte-for-byte identical versions of all of those binaries from source. To learn how to do that, read on.

Building Official Tor Browser Release Binaries

Our build system is based on rbm, which is developed by boklm. rbm creates containers using user_namespaces to provide a clean, controlled, reproducible build environment in a fully automated fashion. We further wrap rbm with our own helper scripts that download and authenticate inputs, and automate building and assembling each component piece of the browser into a final set of output packages for Linux, MacOS, Windows, and Android. This is done with code in the tor-browser-build repository.

This system enables us to provide secure, verifiable, byte-for-byte reproducible builds to ensure the integrity of our binaries and to protect the build process from compromise. We have written a pair of blog posts that describe in more detail why this is important, and the technical details behind how this previously got achieved when using the Gitian system, if you are curious. The new build system based on rbm is working similarly and is facing pretty much the same issues.

To build the Tor Browser, you need essentially a relatively recent x86_64 Linux system. Check out a copy of the tor-browser-build repo with:

git clone https://gitlab.torproject.org/tpo/applications/tor-browser-build.git
cd tor-browser-build

After that you most likely need to install the additional dependencies mentioned in the README file. After installing any remaining dependencies, you should be able to run make, make alpha, make nightly, or make testbuild to build the entire bundle for all four platforms. The build scripts will detect any additional packages or configuration you need to perform on your system.

You will also find a BUILD_ERRORS.txt file under doc/ with further information, should you run into any issues.

Reproducing an Existing Build

The Tor Browser build process is using signed tags for official builds. Stable tags follow the scheme tbb-X.X.X-buildN where X are figures building the version number (like 7.5) and buildN specifies the build number for this particular browser version (e.g. build3). Tags for the alpha releases are similar but contain an a in it like tbb-8.0a1-build3.

Once you know which version you want to reproduce check out the tag containing the latest build number and start doing a make if it is a stable version or make alpha if it is part of the alpha series.

At the end of the build you should end up with a sha256sums-unsigned-build.txt file containing all the SHA-256 sums of the bundles and related packages in alpha/unsigned/your-tor-browser-version (or release/unsigned/your-tor-browser-version, respectively). They should match the official hash sums we have produced.

Be aware that this process is not fully future-proof. In particular, if Debian has updated their development tool chain since the bundles have been built, you may encounter differences between your resulting bundles and the original binaries. This should be rare, however, as we use only the "Long Term Support" or "Oldstable" of Debian in our build VMs. The only reason they should change the tool chain is in the event of serious security issues in the development tools themselves.

Partial Builds

This section is mostly of interest to developers making changes to Tor Browser or its components, and who wish to test their patches.

Building Just Firefox

See the newer wiki page.

Modifying Tor Launcher or Torbutton

Building tor-launcher and torbutton alone are not support anymore. Modify the files in-tree.

Building Android Tor Browser

Android Tor Browser involves a more challenging development process than Tor Browser for desktop platforms (Windows, macOS, Linux).

Android Tor Browser

Android Tor Browser is based on Mozilla Fenix. It's architecture is more modular than desktop Firefox and the previous version of Android Firefox (Fennec).

Android Tor Browser is composed of five main components:

fenix
android-components
application-services
glean
geckoview

These components fit together in a mostly layered way:

Fenix

Fenix is the repository that is the Firefox app. It provides most of the UI for the app and it glues most of the other pieces together.

Android Components

Android Components is, as the name implies, a collection of components for Android. It's goal is providing all of the building blocks in a developer-friendly way that can be used to build web technology - including a web browser.

Application Services

Application Services provides a suite of Mozilla services integration.

Glean

Glean provides a telemetry collection and reporting service.

Geckoview

Geckoview is the heart of the browser. It provides gecko, Mozilla's browser engine, and a (relatively) thin wrapper API for interacting with it and similar to the webview API. See also the Build web apps in WebView guide for some more context.

Setup

General

We modify three out of five repositories. Clone each of them:

git clone https://gitlab.torproject.org/tpo/applications/fenix.git
git clone https://gitlab.torproject.org/tpo/applications/android-components.git
(if needed) git clone https://gitlab.torproject.org/tpo/applications/tor-browser.git

Note: We use the Tor Browser repository for geckoview, as well.

Geckoview

Find the branch you want to build. We'll assume you'll build the current Nightly (Alpha) branch. To find the correct branch name, we refer to tor-browser-build because that holds the authoritative definition of the branch. At the time of writing, the top of the projects/geckoview/config file looks like:

# vim: filetype=yaml sw=2                                                                                                                                                                                  
version: '[% c("abbrev") %]'
filename: 'geckoview-[% c("version") %]-[% c("var/osname") %]-[% c("var/build_id") %].tar.gz'
git_hash: 'geckoview-[% c("var/geckoview_version") %]-[% c("var/torbrowser_branch") %]-2-build2'
tag_gpg_id: 1 
git_url: https://git.torproject.org/tor-browser.git
git_submodule: 1
gpg_keyring: torbutton.gpg
          
var:  
  geckoview_version: 99.0b3
  torbrowser_branch: 11.5

And near the bottom of that file we have:

targets:
  nightly:
    git_hash: 'geckoview-[% c("var/geckoview_version") %]-[% c("var/torbrowser_branch") %]-2'
    tag_gpg_id: 0

The branch we want to build is the git_hash as defined under targets.nightly. This is geckoview-[% c("var/geckoview_version") %]-[% c("var/torbrowser_branch") %]-2, now we simply fill in the variables with concrete values:

geckoview_version is 99.0b3
torbrowser_branch is 11.5

cd tor-browser
git checkout geckoview-99.0b3-11.5-2
git submodule update

Next, run mach bootstrap and let Mozilla's tooling downloading the required packages.

$ ./mach bootstrap

At the first menu, you most likely want option 4. GeckoView/Firefox for Android. Accept the license agreement. You can decline optimizations, if you don't want them.

As an alternative, you can extract the required tooling from tor-browser-build, and add it to the correct PATH.

In both cases, running an Android build locally requires a few environment variables to be defined:

# Firefox needs to know the directory of the JDK, you might use a different one in your system
export MOZ_BUILD_DATE=20220705093820 # This is for 102, but set the correct one, you can find it in android-components/buildSrc/src/main/java/Gecko.kt
export JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64
export ANDROID_HOME=$HOME/Android/Sdk/ # Or .../android-toolchain/android-sdk-linux if you extract android-toolchain from tor-browser-build
export ANDROID_NDK_HOME=$ANDROID_HOME/ndk/android-ndk-r21d # At least this works with android-toolchain from tor-browser-build, not sure about the official Android SDK
export GRADLE_HOME=.../gradle-7.3 # Or the version that we currently use
export LOCAL_DEV_BUILD=1 # Enable some tweaks on our mozconfigs

Android-Components

Create a local.properties in the root (top level) of the repository. Within it, put:

dependencySubstitutions.geckoviewTopsrcdir=/home/user/tor-browser
dependencySubstitutions.geckoviewTopobjdir=/home/user/tor-browser/obj-x86_64-linux-android/

And replace /home/user/ with the correct absolute path for the tor-browser repo.

Fenix

Fenix has a two-step setup process.

First, like android-components, create a local.properties in the root (top level) of the repository. Within it, put:

dependencySubstitutions.geckoviewTopsrcdir=/home/user/tor-browser
dependencySubstitutions.geckoviewTopobjdir=/home/user/tor-browser/obj-x86_64-linux-android/
autoPublish.android-components.dir=/home/user/android-components

And replace /home/user/ with the correct absolute path for the tor-browser and android-components repositories.

Second, we must manually provide the tor-android-service and tor-onion-proxy-library build artifacts. This guide assumes you already built them using tor-browser-build (such as via https://gitlab.torproject.org/tpo/applications/tor-browser/-/wikis/Hacking#reproducing-an-existing-build).

Three files:

service-release.aar
android-release.aar
universal-0.0.3.jar

Copy service-release.aar from the most recent and/or up-to-date build of tor-android-service from tor-browser-build:

$ ls -ltr /home/user/tor-browser-build/out/tor-android-service/ | tail -1
drwxr-xr-x 2 android android    4096 Apr 28 09:12 tor-android-service-0f264c889190-bb3c89
$ cp /home/user/tor-browser-build/out/tor-android-service/tor-android-service-0f264c889190-bb3c89/service-release.aar /home/user/fenix/app/

Again, replace /home/user/ with the appropriate absolute or relative paths.

Similarly, we'll copy the artifacts from tor-onion-proxy-library:

$ ls -ltr /home/user/tor-browser-build/out/tor-onion-proxy-library/ | tail -1
drwxr-xr-x 2 android android 4096 Apr 28 08:07 tor-onion-proxy-library-aeb63ebd079b-691a19
$ cp /home/user/tor-browser-build/out/tor-onion-proxy-library/tor-onion-proxy-library-aeb63ebd079b-691a19/* /home/user/fenix/app/

You can compile these libraries on their own, but this guide does not provide those steps at this time - please add them!

Compiling Geckoview

First, we configure:

$ MOZCONFIG=.mozconfig-android2 ./mach configure  --with-tor-browser-version=tbb-nightly --without-wasm-sandboxed-libraries
[...]
 0:11.83 Creating config.status
 0:12.17 Reticulating splines...
 0:12.67  0:00.53 File already read. Skipping: /home/user/tor-browser/intl/components/moz.build
 0:12.97  0:00.83 File already read. Skipping: /home/user/tor-browser/gfx/angle/targets/angle_common/moz.build
 0:18.14 Finished reading 1086 moz.build files in 1.81s
 0:18.14 Read 58 gyp files in parallel contributing 0.00s to total wall time
 0:18.14 Processed into 6389 build config descriptors in 1.43s
 0:18.14 RecursiveMake backend executed in 2.32s
 0:18.14   2197 total backend files; 2197 created; 0 updated; 0 unchanged; 0 deleted; 22 -> 771 Makefile
 0:18.14 FasterMake backend executed in 0.22s
 0:18.14   9 total backend files; 9 created; 0 updated; 0 unchanged; 0 deleted
 0:18.14 Total wall time: 5.99s; CPU time: 5.78s; Efficiency: 96%; Untracked: 0.22s
 0:18.14 =============
 0:18.14 ADVERTISEMENT
 0:18.14 
 0:18.14 You are building GeckoView. After your build completes, you can open
 0:18.14 the top source directory in Android Studio directly and build using Gradle.
 0:18.14 See the documentation at
 0:18.14 
 0:18.14 https://firefox-source-docs.mozilla.org/mobile/android/geckoview/contributor/geckoview-quick-start.html#build-using-android-studio
 0:18.14 =============
Configure complete!
Be sure to run |mach build| to pick up any changes

Second, we build:

$ MOZCONFIG=.mozconfig-android2 ./mach build
[...]
51:39.42 /usr/bin/notify-send --app-name=Mozilla Build System Mozilla Build System Build complete
To view resource usage of the build, run |mach resource-usage|.
51:39.59 We know it took a while, but your build finally finished successfully!
51:39.59 If you are building Firefox often, SCCache can save you a lot of time. You can learn more here: https://firefox-source-docs.mozilla.org/setup/configuring_build_options.html#sccache
For more information on what to do now, see https://firefox-source-docs.mozilla.org/setup/contributing_code.html
$ MOZCONFIG=.mozconfig-android2 ./mach build binaries && MOZCONFIG=.mozconfig-android2 ./mach gradle geckoview:publishWithGeckoBinariesDebugPublicationToMavenRepository
 0:10.35 Overall system resources - Wall time: 9s; CPU: 28%; Read bytes: 317546496; Write bytes: 7307264; Read time: 2583; Write time: 68                                                                  
To view resource usage of the build, run |mach resource-usage|.                                                                                                                                            
 0:10.36 Your build was successful!
[...]
:machStagePackage> make: Leaving directory '/home/user/tor-browser/obj-x86_64-linux-android/mobile/android/installer'
:machStagePackage> make: Leaving directory '/home/user/tor-browser/obj-x86_64-linux-android/mobile/android/installer'

BUILD SUCCESSFUL in 34s
39 actionable tasks: 5 executed, 34 up-to-date

There are three commands involved:

MOZCONFIG=.mozconfig-android2 ./mach build
MOZCONFIG=.mozconfig-android2 ./mach build binaries
MOZCONFIG=.mozconfig-android2 ./mach gradle geckoview:publishWithGeckoBinariesDebugPublicationToMavenRepository

The resulting, aar (Android Archive) is under obj-x86_64-linux-android/gradle/maven/org/mozilla/geckoview/geckoview-beta-omni/, such as:

$ find obj-x86_64-linux-android/gradle/maven/org/mozilla/geckoview/geckoview-beta-omni/ -name *.aar
obj-x86_64-linux-android/gradle/maven/org/mozilla/geckoview/geckoview-beta-omni/99.0.20220506224557-SNAPSHOT/geckoview-beta-omni-99.0.20220506224557-20220506.233506-1.aar

After you finish building one or more single-arch Geckoview, you should create a fat AAR (even if you only have one architecture).

We have a make target in tools/torbrowser:

make fat-aar ARCHS="armv7" # Specify the architectures you prefer separated by a space

If you are compiling a release version (not beta or nightly), then modify substitute-local-geckoview.gradle like the below patch, adding geckoview-omni as a valid package name:

diff --git a/substitute-local-geckoview.gradle b/substitute-local-geckoview.gradle
index a32dc5ae8a05..f740d7c7effd 100644
--- a/substitute-local-geckoview.gradle
+++ b/substitute-local-geckoview.gradle
@@ -138,6 +138,11 @@ configurations.all { config ->
         'geckoview-beta-omni-arm64-v8a',
         'geckoview-beta-omni-x86',
         'geckoview-beta-omni-x86_64',
+        'geckoview-omni',
+        'geckoview-omni-armeabi-v7a',
+        'geckoview-omni-arm64-v8a',
+        'geckoview-omni-x86',
+        'geckoview-omni-x86_64',
     ]
 
     if (config.isCanBeResolved()) {

Compiling Android-Components

JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64 ANDROID_SDK_ROOT=~/.mozbuild/android-sdk-linux/ ./gradlew assemble
[substitute-local-geckoview] Will substitute GeckoView (geckoview-{nightly,beta}) with local GeckoView (geckoview-default) from /home/user/tor-browser/obj-x86_64-linux-android//gradle/build/mobile/android/geckoview/maven
[substitute-local-geckoview] To update the local GeckoView, run `./mach build binaries && ./mach gradle geckoview:publishWithGeckoBinariesDebugPublicationToMavenRepository` in /home/user/tor-browser
[...]
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':browser-engine-gecko:releaseRuntimeClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':browser-engine-gecko:releaseCompileClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':browser-engine-gecko:debugRuntimeClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':browser-engine-gecko:debugCompileClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':samples-browser:geckoDebugRuntimeClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':samples-browser:geckoDebugCompileClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':samples-compose-browser:releaseRuntimeClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':samples-compose-browser:releaseCompileClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':samples-compose-browser:releaseUnitTestRuntimeClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':samples-compose-browser:releaseUnitTestCompileClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':samples-compose-browser:debugRuntimeClasspath'
[substitute-local-geckoview] Substituting org.mozilla.geckoview:geckoview-omni with local GeckoView org.mozilla.geckoview:geckoview-default-omni in configuration ':samples-compose-browser:debugCompileClasspath'
[...]
BUILD SUCCESSFUL in 7m 33s
6168 actionable tasks: 2704 executed, 1525 from cache, 1939 up-to-date

You may need to specify JAVA_HOME and/or ANDROID_SDK_ROOT. android-components requires java-11, at the time of writing, and you can manually provide the path to a jdk-11 installation if that isn't the default. ANDROID_SDK_ROOT is a path to the required Android SDK (in this case, using the one Mozilla downloaded for geckoview).

Compiling Fenix

$ JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64 ANDROID_SDK_ROOT=~/.mozbuild/android-sdk-linux/ ./gradlew clean app:assembleDebug                                                      
[settings] Loaded local.properties                                                                                                                                                                         
[settings] Disabled auto-publication of application-services. Enable it by settings 'autoPublish.application-services.dir' in local.properties                                                             
[settings] Enabling automatic publication of android-components from: /home/user/android-components                                                                                                     
Contents have not changed, no need to publish                                                                                                                                                              
[settings] Published android-components for local development.                                                                                                                                             
                                                                                                                                                                                                           
> Configure project :app
[...]

BUILD SUCCESSFUL in 7m 56s
50 actionable tasks: 48 executed, 2 up-to-date

Now you should have an apk in app/build/outputs/apk/debug/ (or beta, etc., if built for a different variant).

If you receive an error similar to the below, then please review the above Setup instructions.

> Task :app:dataBindingMergeDependencyArtifactsDebug FAILED                                                                                                 
                                                  
FAILURE: Build failed with an exception.                                                              
                                                                                                                                                                                                           
* What went wrong:                                                                                   
Execution failed for task ':app:dataBindingMergeDependencyArtifactsDebug'.
> Could not resolve all files for configuration ':app:debugCompileClasspath'.
   > Failed to transform service-release.aar to match attributes {artifactType=android-databinding}.                                                                                                       
      > Execution failed for IdentityTransform: /home/user/fenix/app/service-release.aar.
         > File/directory does not exist: /home/user/fenix/app/service-release.aar
   > Failed to transform android-release.aar to match attributes {artifactType=android-databinding}.
      > Execution failed for IdentityTransform: /home/user/fenix/app/android-release.aar.
         > File/directory does not exist: /home/user/fenix/app/android-release.aar

Final Bundling

Now, we must include three components in the apk we built:

Noscript
https-everywhere
allowed_addons.json

Again, we use the assets from tor-browser-build:

$ mkdir -p assets/extensions
$ cp /home/user/tor-browser-build/out/tor-browser/noscript_security_suite-11.4.5-an+fx.xpi assets/extensions/'{73a6fe31-595d-460b-a920-fcc0f8843232}.xpi'
$ unzip -d assets/extensions/https-everywhere ../tor-browser-build/out/https-everywhere/https-everywhere-2021.7.13-0fc77a.xpi
Archive:  ../tor-browser-build/out/https-everywhere/https-everywhere-2021.7.13-0fc77a.xpi
  inflating: assets/extensions/META-INF/cose.manifest  
  inflating: assets/extensions/META-INF/cose.sig   
  inflating: assets/extensions/META-INF/manifest.mf
[...]
$ cp ../tor-browser-build/projects/tor-browser/allowed_addons.json assets/
$ zip -r app/build/outputs/apk/debug/app-x86_64-debug.apk assets/                                                                                                                     
updating: assets/allowed_addons.json (deflated 67%)                                  
updating: assets/ (stored 0%)                                                                        
  adding: assets/extensions/ (stored 0%)                                                             
  adding: assets/extensions/{73a6fe31-595d-460b-a920-fcc0f8843232}.xpi (deflated 2%)               
  adding: assets/extensions/https-everywhere/ (stored 0%)                            
  adding: assets/extensions/https-everywhere/wasm/ (stored 0%)

Finally, re-align the zip and sign it. Here we use the QA signing key in tor-browser-build.

$ ~/.mozbuild/android-sdk-linux/build-tools/31.0.0/zipalign -vp 4 app/build/outputs/apk/debug/app-x86_64-debug.apk app-x86_64-debug-unsigned.apk
[...]
Verification succesful
$ ~/.mozbuild/android-sdk-linux/build-tools/31.0.0/apksigner sign --verbose --min-sdk-version 21 --ks /home/user/tor-browser-build/projects/tor-browser/android-qa.keystore --out app-x86_64-debug-qa.apk --in app-x86_64-debug-unsigned.apk --ks-key-alias androidqakey --key-pass pass:android --ks-pass pass:android
Signed

Running Multiple Tor Browsers

Now that you have a developer build (or several builds), you probably want to know how to run more than one of them at once. There are two main ways to do this: reusing an existing Tor process, and launching Tor process on a new pair of SOCKS and Control ports.

Using an Existing Tor Process

Let's assume that Tor process is listening on port 9150 for SOCKS, and 9151 for the control port.

export TOR_SOCKS_PORT=9150
export TOR_CONTROL_PORT=9151
export TOR_CONTROL_COOKIE_AUTH_FILE=~/tbb/tor-browser_en-US/Browser/TorBrowser/Data/Tor/control_auth_cookie
export TOR_SKIP_LAUNCH=1

cd $INSTDIR # from the 'Partial Builds' section above
./start-tor-browser.desktop

Launching Tor with an Alternate SOCKS and Control port

If you need to test Tor Launcher changes, you probably want to launch the Tor process too. Here's a quick hack to put that on a different port pair (9250 and 9251):

export TOR_SOCKS_PORT=9250
export TOR_CONTROL_PORT=9251
unset TOR_SKIP_LAUNCH
unset TOR_CONTROL_COOKIE_AUTH_FILE

cd $INSTDIR   # From the 'Partial Builds' section above
./start-tor-browser.desktop

Tor Browser Team Communication and Organizational Patterns

The Tor Browser development team is very geographically distributed. We use a few different written forms of communication to discuss development over the Internet: Mailing lists, IRC, and this bug tracker. We also hold weekly IRC meetings.

Communication Mechanisms and Meetings

The mailinglist for Tor Browser development discussion is tbb-dev. You can also subscribe to the list of Tor Browser code commits via tbb-commits. All updates to Tor Browser specific bugs are sent to tbb-bugs. Release tags and test builds are posted to tor-qa for community review and testing.

Our primary mode of day-to-day communication is the #tor-dev IRC channel on irc.oftc.net (port 6697 is ssl). We hold weekly meetings on this IRC channel at 19:00 UTC on Mondays. For details on our meeting format, please see the original meeting announcement post (note however that the time has changed since that posting).

How we use Trac

For historical reasons, Tor Browser tickets are spread across several Trac components: "Tor bundles/installation", "TorBrowserButton", "Firefox Patch Issues", and "Tor Launcher". We are considering consolidating many of these components and switching to keywords instead, but that hasn't happened yet.

Trac Keywords

What follows is a partial list of trac keywords we use to categorize issues, independent of the component they actually arise in.

tbb-crash:: Tickets that represent reported crash or hang issues tbb-usability:: Tickets that represent usability issues. Has many subcategories as suffixes of tbb-usability. tbb-usability-stoppoint:: Tickets that represent usability issues that cause users to be unable to use TBB (this is a subset of the previous query) tbb-helpdesk-frequent:: Tickets that represent frequently encountered support issues or blog/twitter commentary tbb-linkability:: Tickets that represent a violation of our identifier unlinkability Privacy Requirement. tbb-fingerprinting:: Tickets that represent a violation of our fingerprinting unlinkability Privacy Requirement. There are many subcategories of this tag as suffixes. tbb-disk-leak:: Tickets that represent a violation of our Disk Avoidance Security Requirement. tbb-newnym:: Tickets for problems with "New Identity" tbb-testcase:: Tickets for which we would like to have an automated testcase to prevent regressions. tbb-security:: Tickets for hardening TBB against exploitation. tbb-needs:: Tickets in other Tor components that TBB needs solved. tbb-mobile:: Tickets for work on Tor Browser for mobile in particular tbb-spec:: Tickets for work on Tor Browser's design documentation tbb-security-slider:: Tickets for work on Tor Browser's security slider tbb-update:: Tickets for work on Tor Browser's update related code. tbb-parity:: Tickets for work on feature parity between Tor Browser on different platforms. tbb-backport:: Tickets that we could consider for backporting from the current alpha to the current stable series. The keyword gets cleared with every new major stable release and the cycle start from the beginning.

In addition to this list, if you would like someone to review a patch, you should set the state of that ticket to "needs review" and tag it that that person's name, followed by the year, the month, and the letter 'R'. For example: MikePerry201311R.

Design and Core Components

Ok, so you've got the lay of the land now, and want to really dive in. Here's how everything is organized.

Design Document

At a high level, Tor Browser development is driven by the design document: The Design and Implementation of the Tor Browser. This document specifies the Design Requirements and Philosophy that guides our development decisions and our modifications to Firefox, provides an adversary model, and provides a high level description of the actual changes we have made to Firefox.

Component Source Repositories

The Tor Browser is actually built from several components. Here are the main ones specific to the browser itself.

Firefox Branch Repo

We maintain a branch of the latest Firefox "Extended Support Release" (ESR) series, to which we have applied multiple patches to satisfy our design requirements and build security needs.

These branches live in the tor-browser git repo. The branches are named for the Firefox version they are based off of, along with an integer signifying a rebase number. To learn which branch a particular build uses, inspect its version file. The version file lists a tag for the specific commit used. This tag is derived from the branch name and an additional specific build number.

Torbutton

Torbutton is an addon with a long and storied history. It originated as ProxyButton (a simple Firefox addon to toggle proxy settings), which was rethemed by Scott Squires and configured specifically for Tor's proxy settings. After that initial work, Mike Perry began development to address the numerous security issues that arose when browser state from non-Tor activity leaked into Tor browsing mode, and vice-versa. This toggle mode was deprecated in favor of a standalone browser several years back.

As a result, Torbutton contains a lot of cruft code specific to the toggle behavior that has not yet been removed, but is otherwise inactive. However, it still provides a few privacy features by way of observers and other extension-level changes to Firefox to improve privacy and Tor security.

Tor Launcher

Tor Launcher is a Firefox addon that acts as a Tor Controller. It handles launching and configuring Tor for use with the browser. It also is compatible with Thunderbird, InstantBird, and XULRunner, and is used by the Tails project as well.

HTTPS-Everywhere

HTTPS-Everywhere contains tens of thousands of URL rewrite rules to enforce HTTPS for sites that support both HTTP and HTTPS URL schemes.

NoScript

We don't modify NoScript directly, however we do have a number of preferences changes to it and other addons in the tor-browser-bundle preferences file in the bundle layout directories.

If you're interested in bisecting or otherwise tracking down a particular NoScript change, bug, or issue, avian2 maintains a complete git repository for NoScript, with one commit per NoScript release (including alphas, betas, and rc releases).

Pluggable Transports

Tor Browser includes several pluggable transports, which are a network traffic transformation layer to help avoid censorship and filtering mechanisms. If you are interested in getting your own pluggable transport added to the bundle, the FTE transport work is a good example to follow.

The original ticket for FTE is a good starting point. It resulted in a clean branch that merged easily.

Pluggable Transport Bridges are specified in the bridge_prefs.js configuration file in the Bundle Skeleton directory.

Debugging the Tor Browser

There are a few different ways to debug the Tor Browser, depending on the component involved. We'll focus on the extensions and the browser itself here.

Enabling debug logs in extensions

To enable extension debug logging, set these preferences in your about:config:

SETTING NAME	VALUE
extensions.torbutton.loglevel	2
extensions.torbutton.logmethod	0
extensions.https_everywhere.LogLevel	2
extensions.https_everywhere.log_to_stdout	true
extensions.torlauncher.loglevel	2
extensions.torlauncher.logmethod	0

Lower levels are more verbose, but if you go much below 2, you will likely be overwhelmed and/or the browser will be extremely slow.

If you want to save your logs to a file, you need to use the --log argument to start-tor-browser.desktop. It takes an optional filename. Without a filename, it writes tor-browser.log in the current directory:

$ ./start-tor-browser.desktop --log
$ tail -f tor-browser.log

Offline Logging/Tracing

Sometimes you need to resort to printf style debugging (for instance, on platforms which do not have debug symbols) or you are diagnosing a race condition that's highly sensitive to timing. In such cases, check out TbbLogger ( https://github.com/pospeselr/tbblogger ).

Apply the TbbLogger.patch to your firefox sources and you will be able to include the TbbLogger.h header throughout the firefox code base. This header defines two macros for your enjoyment: TBB_LOG(format-string, ...) and TBB_TRACE().

The TBB_LOG macro allow tracing using fmtlib ( http://fmtlib.net/latest/syntax.html ) formatting with some extra debug info: timestamp, parent/child content process, thread id, and log location. The TBB_TRACE macro does not include any message. This information, plus your format-string and args, are serialized to disk on a background thread as a binary blob. Logs are converted to plain-text via an offline 'aggregate' tool which will convert the binary blob to formatted messages sorted by timestamp. The timestamps ensure that messages are written in the order they actually happened, even between the parent and child content processes.

Example Usage

Source

   ...
    #include "TbbLogger.h"
    ...
    void function_name()
    {
        ...
        TBB_TRACE();
        int some_int = 100;
        double some_double = 34.0;
        TBB_LOG("This is some logging %i %f", some_int, some_double);  
        ...
    }

Aggregate

$ ./aggregate /tmp/firefox/*.bin 
[0.000323][Parent][29958] function_name in Test.cpp:18 
[0.000324][Parent][29958] function_name in Test.cpp:22 This is some logging 100 34.000000

Using the Javascript Debugger

XXX: Write or link to some documentation on using Venkman/JSD for extension debugging. There are two options for this: Venkman and the in-browser debugger. For TBB pre-5.0, Venkman was the way (https://addons.mozilla.org/en-us/firefox/addon/javascript-debugger/). However, it is no longer supported. Instead, the built-in debugger must be used: https://developer.mozilla.org/en-US/docs/Debugging_JavaScript#JavaScript_Debugger

Debugging on Windows

Firstly, ignore the 'Using gdb' section immediately after this one, that's only for Linux. Then go to DebuggingOnWindows

Using gdb

Using Debug Symbols

If you're going to use GDB to debug an issue, the first thing you want is debug symbols. Tor Browser builds detached debug symbols for tor and firefox.

In the bundle release download directory there should be a tor-browser-linux64-debug.zip file. Unfortunately, the directory structure of the debug zip doesn't exactly match what you need in order for gdb to find the symbols automatically. For the tor-browser-linux symbols, unzip the file in the bundle root directory, and then relocate it to the .debug subdirectory of Browser, like so:

$ cd tor-browser_en-US
$ wget https://dist.torproject.org/torbrowser/8.5a11/tor-browser-linux64-debug.tar.xz
$ tar xavf tor-browser-linux64-debug.tar.xz
$ mv Debug/Browser Browser/.debug
$ gdb ./Browser/firefox.real

At this point, gdb should find all of the Firefox symbols automatically upon every invocation, and you can either attach to an existing process ID or launch firefox directly, as described in the following sections below.

Attaching an already running TBB

You can attach a gdb instance to an already running TBB firefox process. To do this, find the pid of your running TBB firefox.real, then tell gdb to attach the running process (note that on some systems you may need to run gdb as root for this to work):

$ for p in `pgrep firefox.real` ; do ps -v $p ; done
[...find the pid for your TBB firefox...]
$ gdb ./Browser/firefox.real
(gdb) attach <pid>

Starting firefox from inside gdb

Assuming you run an alpha build, starting firefox inside gdb:

 $ gdb ./Browser/firefox.real
 (gdb) set env LD_LIBRARY_PATH=Browser/TorBrowser/Tor
 (gdb) set env SELFRANDO_skip_shuffle=
 (gdb) run -profile Browser/TorBrowser/Data/Browser/profile.default

Generating and debugging core files

If you have a condition that crashes Tor Browser in an unreliable way, one helpful step is to generate a core file for crashes that do happen. To do this, before launching Tor Browser, run:

$ ulimit -c unlimited

Then, when Tor Browser crashes, a core file should show up in Browser/core. To debug this core, run:

$ gdb ./Browser/firefox ./Browser/core

You can then use the usual gdb commands (backtrace, print, up, down, etc) to inspect the stack, variables, and program state at the time of the crash.

Debugging ASan/selfrando builds

If you need to debug a hardened build that includes ASan and selfrando you have two options.

Temporarily disable selfrando

If you set the environmental variable SELFRANDO_skip_shuffle, selfrando will be disabled and gdb will work as usual. E.g.:

$ gdb -ex "set env LD_LIBRARY_PATH=$PWD/Browser/TorBrowser/Tor" -ex "set env SELFRANDO_skip_shuffle=" \
	-ex 'set env ASAN_OPTIONS="detect_leaks=0,abort_on_error=1"' -ex "set env NSS_DISABLE_HW_AES=1" \
	--args Browser/firefox -profile Browser/TorBrowser/Data/Browser/profile.default/

Convert ASan's stack trace message

This method can be used only to debug a crash. Start Tor Browser with Browser/start-tor-browser -v. After the browser crashes, you will see one or more stack traces that look like this:

==3896==ERROR: AddressSanitizer: heap-use-after-free on address 0x6040003b85e0 at pc 0x7f5dff50f35d bp 0x7ffe516e3a90 sp 0x7ffe516e3a88
READ of size 4 at 0x6040003b85e0 thread T0
SRAT init
    #0 0x7f5dff50f35c  (/path/to/directory/tor-browser/Browser/libxul.so+0x4af0a9a)
    #1 0x7f5dfe153916  (/path/to/directory/tor-browser/Browser/libxul.so+0x4af0d32)
    #2 0x7f5e001ae7f6  (/path/to/directory/tor-browser/Browser/libxul.so+0x392d7e8)
[...]
    #43 0x418d98  (/path/to/directory/tor-browser/Browser/firefox+0x4089dc)
    #44 0x7f5e0b0d8f44 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21f44)
    #45 0x41e9dc  (/path/to/directory/tor-browser/Browser/firefox+0x408e34)

To get a meaningful stack trace you need to install a symbolizer (you can install clang and use llvm-symbolizer). Then, copy the relevant text from ASan's output, pipe it trough [convert-asan-to-symbolizer.py convert-asan-to-symbolizer.py] and then into the symbolizer. E.g.:

$ xsel -b | ./convert-asan-to-symbolizer.py | llvm-symbolizer-3.4

The script assumes that debug information is available in Browser/.debug (see [#UsingDebugSymbols Using Debug Symbols]).

Using dtrace

Dtrace is a very powerful tracing and debugging system that requires kernel support, however all the grown-up Operating Systems support it (not supported by Linux). Like many of the powerful creations of Unix, dtrace immediately gave rise to an orgy of one-liners. That is, one-line dtrace programs that perform a useful task! Like awk, there are many such dtrace one-liners that people have documented and are still useful today, often with little or no modification. In fact, you can utilize both dtrace and awk in the same command pipeline to create something even more expressive!

The IllumOS (the new OpenSolaris) kernel has support for Linux zones which can run native x86 32bit and 64bit binaries in an isolated environment. They have done such a good job at this Linux binary system call emulation that it can run all the normal stuff including systemd and other monstrosities such as htop. ;-p My Debian 8 image indeed acts like a normal Debian 8 system... although it is definitely not running the Linux kernel.

The host's global zone can be used to dtrace native Linux and Solaris zones. Tor Browser Bundle runs fine using the Linux zones.

Isolating tor applications with SmartOS

onion -> noVNC http -> vnc4server -> tbb

more dtrace examples [https://wiki.smartos.org/display/DOC/DTrace]

dtrace examples for Tor Browser Bundle

Many of these examples collect dtrace probe information until the operator hits control-c. I found many dtrace exmamples. Here's some that might be useful:

Which files does firefox open?

dtrace -n 'lx-syscall::open*:entry /execname == "firefox"/ { printf("%s %s", execname, copyinstr(arg0)); }
'
dtrace: description 'lx-syscall::open*:entry ' matched 6 probes
CPU     ID                    FUNCTION:NAME
  0   3874                       open:entry firefox /dev/urandom
  0   3874                       open:entry firefox /home/human/tor-browser_en-US/Browser/TorBrowser/Tor/libcanberra.so.0
  0   3874                       open:entry firefox /etc/ld.so.cache
  0   3874                       open:entry firefox /lib/x86_64-linux-gnu/libcanberra.so.0
  0   3874                       open:entry firefox /usr/lib/x86_64-linux-gnu/libcanberra.so.0
  0   3874                       open:entry firefox /lib/libcanberra.so.0
  0   3874                       open:entry firefox /usr/lib/libcanberra.so.0
  0   3874                       open:entry firefox /home/human/tor-browser_en-US/Browser/TorBrowser/Tor/libcanberra.so.0
  0   3874                       open:entry firefox /etc/ld.so.cache
  0   3874                       open:entry firefox /lib/x86_64-linux-gnu/libcanberra.so.0
  0   3874                       open:entry firefox /usr/lib/x86_64-linux-gnu/libcanberra.so.0
  0   3874                       open:entry firefox /lib/libcanberra.so.0
  0   3874                       open:entry firefox /usr/lib/libcanberra.so.0
  0   3874                       open:entry firefox /dev/urandom
  0   3874                       open:entry firefox /dev/urandom
^C

syscall frequency count

dtrace -n 'lx-syscall:::entry /pid == 44622/ { @num[probefunc] = count(); }'
dtrace: description 'lx-syscall:::entry ' matched 676 probes
^C

  read                                                            725
  write                                                           725
  writev                                                         1400
  futex                                                          3548
  poll                                                           5686
  recvmsg                                                        6911
  clock_gettime                                                 17440

function and module top 10 frequency count lx_proc_func_count.d

pid$target:::entry { 
@a[probemod,probefunc] = count(); 
}
END { trunc(@a,10); }

./lx_proc_func_count.d -p 44622
dtrace: script './lx_proc_func_count.d' matched 30865 probes
^C
CPU     ID                    FUNCTION:NAME
  0      2                             :END 

  firefox                                             realloc                                                       31609
  libmozalloc.so                                      moz_xmalloc                                                   33383
  libmozalloc.so                                      moz_free                                                      36504
  firefox                                             malloc                                                        50687
  firefox                                             free                                                          54604
  libpthread.so.0                                     pthread_self                                                  58444
  libpthread.so.0                                     pthread_getspecific                                           69741
  libpthread.so.0                                     pthread_mutex_unlock                                         204393
  libpthread.so.0                                     pthread_mutex_lock                                           204394
  libpthread.so.0                                     __pthread_mutex_unlock_usercnt

lxsockopt.d

 
#pragma D option quiet
 
/**
PROTO values can be found here:
https://en.wikipedia.org/wiki/List_of_IP_protocol_numbers
SOCKOPT values can be found here:
https://github.com/joyent/illumos-joyent/blob/master/usr/src/lib/brand/lx/lx_brand/common/socket.c
*/
BEGIN
{
        printf("%6s %20s %5s %s\n", "PID", "NAME", "PROTO", "SOCKOPT");
}
 
lx-syscall::setsockopt:entry
{
        printf("%6d %20s %5d %d\n", pid, execname, arg1, arg2);
}

./lxsockopt.d 
   PID                 NAME PROTO SOCKOPT
 44622              firefox     6 1
 15388                  tor     1 2
 44622              firefox     6 4
 44622              firefox     6 5
 44622              firefox     6 6
 44622              firefox     6 4
 44622              firefox     6 5
 44622              firefox     6 6
 44622              firefox     1 9
 44622              firefox     6 4
 44622              firefox     6 5
 44622              firefox     6 6
 44622              firefox     1 9

track malloc allocations

dtrace -n 'pid8880::malloc:entry { printf ("Firefox is asking for %d bytes", arg0); }'  

  0  74421                     malloc:entry Firefox is asking for 24 bytes
  0  74421                     malloc:entry Firefox is asking for 48 bytes
  0  74421                     malloc:entry Firefox is asking for 16 bytes
  0  74421                     malloc:entry Firefox is asking for 32 bytes
  0  74421                     malloc:entry Firefox is asking for 16 bytes
  0  74421                     malloc:entry Firefox is asking for 8176 bytes

in real-time, find all the code modules which utilize malloc:

  dtrace -l -n 'pid$1::malloc:entry' 1774

     ID   PROVIDER            MODULE                          FUNCTION NAME
   74421    pid1774           firefox                            malloc entry
   74578    pid1774      LMfd`ld.so.1                            malloc entry
   75306    pid1774 LMfd`libmapmalloc.so.1                            malloc entry
   76053    pid1774    LMfd`libc.so.1                            malloc entry
   84541    pid1774         libc.so.6                            malloc entry
   85794    pid1774 ld-linux-x86-64.so.2                            malloc entry

Bisecting

If you found a bug and want to start bisecting to find the exact commit which introduced the problem you have three major cases to consider.

The easy case

You found your bug is part of either Torbutton, Tor Launcher or HTTPS-Everywhere. In this case you check out the respective repository and do the usual bisecting there. To test the various revisions you can take a clean Tor Browser and load the .xpi's into it. Theoretically, this would work in the NoScript case as well but unfortunately there is no public version control system available and thus if you found a bug in NoScript you need to identify the version it showed first up manually and file a ticket.

The medium difficult case

Okay, you ruled out a bug in one of the extensions we ship and determined it got introduced by one of our Tor Browser patches or changes to the bundling/build process (testing whether the bug occurs in a corresponding vanilla Firefox is helpful here). The first thing you are doing now is finding out which Tor Browser version is the one that introduced the bug. Using the Tor Browser archive is a good starting point. If you found the culprit and the bug did not get introduced while switching to a new Firefox ESR (the next section deals with the switching case) chances are high that you don't need to bisect at all. Comparing the changelogs between the last version without the bug and the first version with the bug should be enough in this case. But if the changelogs don't ring a bell and you suspect this is a bug introduced by the build process/bundling looking at the changes introduced in the tor-browser-bundle repository between the two Tor Browser releases should reveal the bad commit. If the changelogs don't help and you suspect an issue with one or more of our Tor Browser patches you need to clone the tor-browser repository and do a normal bisect following the Partial Builds strategy outlined above between the last tor-browser patch of the good Tor Browser and the last tor-browser patch that got into the bad Tor Browser.

The tricky case

The patchset effectively did not change and you are only switching to a new ESR. There could be three reasons for the bad Tor Browser then. The first one: rebasing one or more patches went wrong. The second one: some change in the new ESR is causing the trouble. The third one: a combination of the first two. The strategy to deal with this group of cases is to rule out the first one (and thus the third one as well) and then narrow down the possible patches that could be affected by changes in the new ESR. These patches in turn are applied during bisecting the commits in the mozilla-central repository that made it into the bad Tor Browser.

Testing in TaskCluster

If you suspect there is an issue with Tor's toolchain, you can use Tor's toolchain in taskcluster relatively easily, like so: https://hg.mozilla.org/try/rev/bbee5fef95a86824e37a01162cc3ee0a56b1ed3a

QA and Testing

Some automated tests are run on nightly builds, and new releases. The main page for the results is http://test-reports.tbb.torproject.org/reports/.

If you want to run the test suite yourself, read the installation instructions, and the usage instructions. You can also learn how to add a new test.

The different categories of tests we are running are described below.

Tor Browser Test Suite

This test suite contains a series of tests to check a Tor Browser Bundle. It is used to check different things:

the binaries included in the bundle are correctly linked and compiled
the tor daemon is working, with bridges, some pluggable transports and with an http proxy
some mozill and selenium tests

The list of tests is defined in TBBTestSuite/TestSuite/BrowserBundleTests.pm. Documentation for adding new tests is available.

This test suite is automatically run in the following cases:

when a new nightly build is available on https://people.torproject.org/~linus/builds/. An email of the results is sent to a list of people defined in config/linus-nightly. You can ask me if you want to be added to this list.
when a new release is tagged on git and available on https://people.torproject.org/~user/builds/$version/. The result of the tests is emailed to tor-qa@lists.torproject.org.
when a Tor Browser developer created a tbb-qa.yml file to request a build to be test. The result of the tests is emailed to the developer requesting the tests. See the section below for details about requesting tests on custum builds.

VirusTotal uploads

The Windows version of the Tor Browser .exe file is uploaded to virustotal.com to check it with different antivirus. All executable files included in the archive are also uploaded.

The uploads are automatically done in the following cases:

when a new nightly build is available on https://people.torproject.org/~linus/builds/. The results are available on http://test-reports.tbb.torproject.org/reports/index-browserbundle_virustotal.html. No emails are sent at the moment (you can ask me if you are interested to receive them).
when a new release is tagged on git and available on https://people.torproject.org/~user/builds/$version/. The results are sent to tor-qa@lists.torproject.org.

Browser Unit Tests

The Browser Unit Tests are the tests which are included in the Mozilla sources tree (xpcshell and mochitests). The Tor Browser patches can add new tests to be run. Before running those tests, we need to build the sources tree.

We are able to run those tests on a series of commits, and display the differences in the results between each commits and its ancestor.

It is not currently run automatically. In the future, it should be possible to specify a commit or branch to be tested, by editing the tbb-qa.yml file. Until then, you can ask me to edit the config file to test a specific branch or commit.

Rebasing Tests

A prototype for a rebasing tests has been made. The goal is to try to automatically rebase all Tor Browser patches on the master branch of gecko-dev.

It is not yet run automatically.

Requesting testing of a custom build using the tbb-qa.yml file

To request a custom build to be tested, you need an account on people.torproject.org and be listed in the config/testrequests file (ask me if you want to be added).

Upload your build to perdulce in directory ~public_html/builds/x.y.z-featureA

Create a file public_html/builds/tbb-qa.yml with permission 744 and a list of build directory names using the YAML syntax:

 ---
 - x.y.z-featureA

You should receive an email on your @torproject.org email address when the tests finished running. Make sure to include a proper sha256sums.txt file and its signature in the respective build directory.

The tbb-qa.yml file can also be used to request other types of tests. Instead of adding a string which is a directory name in your builds directory, you can add a hash table containing the options for your test requests and a 'type' key containing the type of tests you want to run.

For instance the following tbb-qa.yml file can be used to request a test of type 'browserunit' (Tor Browser unit tests) on a specific commit:

---
- type: browserunit
  commit: e1a8bafb44367592b

The following types of tests are available:

Tor Browser Unit Tests (xpcshell and mochitest)

type name: browserunit

Options:

commit: the commit that you want to build and run tests on. This can be a commit hash, tag or branch.
esr_branch: using this option means that you want all commits from the Mozilla ESR branch to the selected commit to be tested. Example: esr31.
git_url: the URL of the git repository containing the selected commit. If unspecified, https://git.torproject.org/tor-browser.git is used by default.

Android

There are two supported way for testing (and developing) Tor Browser on Android.

Command line Mozilla provide support for building and running the test suits on an emulator or a device via mach. This is the easiest and most straight forward method right now.
Android Studio Android Studio provides a nice IDE for developing Android Apps. You can follow the initial build instructions for Android on this page, and then go to Mozilla's [Studio instructions] section: Developing Firefox for Android in Android Studio. Following those instructions should get you up and running.

A note on Android emulators. Mozilla Fennec required the ARM processor support NEON. Unfortunately, it seems like Android kernels compiled for older APIs don't support this (?). It's annoying. As an example, compare the CPU Features:

a stock armeabi-v7a API 18 emulator does not support that extension:

root@generic:/ # uname -a
/system/bin/sh: uname: not found
126|root@generic:/ # cat /proc/sys/kernel/osrelease                            
3.10.0+ 
root@generic:/ # cat /proc/sys/kernel/ostype                                   
Linux
root@generic:/ # cat /proc/sys/kernel/version                                  
#8 SMP PREEMPT Mon May 23 14:53:39 PDT 2016
root@generic:/ # cat /proc/sys/kernel/hostname                                 
localhost
root@generic:/ # cat /proc/cpuinfo                                             
processor	: 0
model name	: ARMv7 Processor rev 1 (v7l)
BogoMIPS	: 125.00
Features	: swp half thumb fastmult vfp edsp vfpv3 tls vfpv4 idiva idivt vfpd32 evtstrm 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x2
CPU part	: 0xc0f
CPU revision	: 1

Hardware	: Dummy Virtual Machine
Revision	: 0000
Serial		: 0000000000000000

a stock armeabi-v7a API 24 emulator does support that extension:

generic:/ $ uname -a
Linux localhost 3.10.0+ #1 SMP PREEMPT Wed May 18 00:25:13 UTC 2016 armv7l
generic:/ $ cat /proc/cpuinfo
processor	: 0
model name	: ARMv7 Processor rev 1 (v7l)
BogoMIPS	: 125.00
Features	: swp half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 evtstrm 
CPU implementer	: 0x41
CPU architecture: 7
CPU variant	: 0x2
CPU part	: 0xc0f
CPU revision	: 1

Hardware	: Dummy Virtual Machine
Revision	: 0000
Serial		: 0000000000000000

FPCentral

FPCentral is a tool which was created by Pierre Laperdrix as a Google Summer of Code project. We use this tool to detect changes in the fingerprint of new Tor Browser releases.

An instance of FPCentral is available at the following URL: https://fpcentral.tbb.torproject.org/

The git repository containing the sources is at: https://gitweb.torproject.org/fpcentral.git/

The tests for the different fingerprint attributes are defined in the fingerprint/attributes directory. If you want to add a new test, you will need to create a javascript file containing a function returning an attribute value, and a json file describing this attribute. See the README.md file for more details.

When you run the fingerprint tests using Tor Browser, it should tell you if all attributes have an acceptable value. The list of acceptable values for each attribute is defined in the fingerprint/acceptable/torbrowser70.json file. When adding a new attribute definition, you should also define an acceptable value in this file.

Adding New Default Bridges

The anti-censorship team takes care of adding, maintaining, and monitoring default bridges. There's a wiki page that details the process of adding default bridges to Tor Browser.

The Tor Browser Hacking Guide

Ways to Build Tor Browser

Nightly Builds

Building Official Tor Browser Release Binaries

Reproducing an Existing Build

Partial Builds

Building Just Firefox

Modifying Tor Launcher or Torbutton

Building Android Tor Browser

Android Tor Browser

Fenix

Android Components

Application Services

Glean

Geckoview

Setup

General

Geckoview

Android-Components

Fenix

Compiling Geckoview

Compiling Android-Components

Compiling Fenix

Final Bundling

Running Multiple Tor Browsers

Using an Existing Tor Process

Launching Tor with an Alternate SOCKS and Control port

Tor Browser Team Communication and Organizational Patterns

Communication Mechanisms and Meetings

How we use Trac

Trac Keywords

Design and Core Components

Design Document

Component Source Repositories

Firefox Branch Repo

Torbutton

Tor Launcher

HTTPS-Everywhere

NoScript

Pluggable Transports

Debugging the Tor Browser

Enabling debug logs in extensions

Offline Logging/Tracing

Example Usage

Source

Aggregate

Using the Javascript Debugger

Debugging on Windows

Using gdb

Using Debug Symbols

Attaching an already running TBB

Starting firefox from inside gdb

Generating and debugging core files

Debugging ASan/selfrando builds

Temporarily disable selfrando

Convert ASan's stack trace message

Using dtrace

dtrace examples for Tor Browser Bundle

Bisecting

The easy case

The medium difficult case

The tricky case

Testing in TaskCluster

QA and Testing

Tor Browser Test Suite

VirusTotal uploads

Browser Unit Tests

Rebasing Tests

Requesting testing of a custom build using the tbb-qa.yml file

Tor Browser Unit Tests (xpcshell and mochitest)

Android

FPCentral

Adding New Default Bridges

Other Resources