Development-Information/Codebases.md

+Like many large software projects, Tor Browser integrates many distinct codebases.
+
+# Tor Browser
+
+[Repository](https://gitlab.torproject.org/tpo/applications/tor-browser)
+
+Tor Browser is based on Firefox, and this repository contains our fork of Mozilla's [mozilla-central](https://hg.mozilla.org/mozilla-central/).
+From this code, we build both Tor Browser for desktop (TBB, Tor Browser Bundle) and [GeckoView](https://mozilla.github.io/geckoview/), which is the rendering engine for Tor Browser for Android (TBA).
+
+Every time a new Firefox version is released, we create four new branches on this project, then we reapply our patch set on top of it.
+
+Therefore, the repository does not have a mainline, and we work concurrently on four branches:
+
+1. Tor Browser stable for desktop
+2. Tor Browser alpha for desktop
+3. Geckoview stable
+4. Geckoview alpha
+
+While Mozilla keeps the codebase for Firefox and GeckoView united, we keep it separate for some reasons:
+
+* desktop is based on the ESR channel, Android on the rapid release one;
+* while many patches are the same, others are incompatible between the two platforms or are implemented differently because of architectural differences.
+
+# Torbutton
+
+[Repository](https://gitlab.torproject.org/tpo/applications/torbutton)
+
+Torbutton is the component in Tor Browser that takes care of application-level security and privacy concerns in Firefox.
+
+It was born as a Firefox addon, but now it is a built-in extension.
+
+# Tor Launcher
+
+[Repository](https://gitlab.torproject.org/tpo/applications/tor-launcher)
+
+Tor Launcher controls the Tor process underlying the browser networking.
+
+It was born as an addon and also provided the network configuration UI. Now it is a built-in extension, and the configuration UI has been moved into the Tor Browser repository.
+
+_Not to be confused with torbrowser-launcher, which is not an Application Team's project._
+
+# Fenix
+
+[Repository](https://gitlab.torproject.org/tpo/applications/fenix)
+
+Fenix is the codename of Firefox for Android. This repository contains the code to build Tor Browser Android from the patched GeckoView and Android Components.
+
+Like other repositories, it does not have a mainline. Each branch is a version released by Mozilla, with our patch set applied.
+
+# Android Components
+
+[Repository](https://gitlab.torproject.org/tpo/applications/android-components)
+
+[Mozilla Android Components](https://mozac.org/) is a collection of independent, reusable Android library components to make it easier to build browsers and browser-like applications.
+
+It is another of the pieces used to build TBA.
+
+Like Fenix and GeckoView, each branch is a MozAC version, plus Tor Browser patches.
+
+# Tor Android Service
+
+[Repository](https://gitweb.torproject.org/tor-android-service.git/)
+
+It is the Tor controller for Android.
+
+# Tor Browser Build
+
+[Repository](https://gitlab.torproject.org/tpo/applications/tor-browser-build)
+
+It is the repository we use to create reproducible builds of Tor Browser for desktop and Android and manage all their dependencies.
+
+It is based on [RBM (Reproducible Build System)](https://rbm.torproject.org/).
+
+# Tor Browser Bundle Testsuite
+
+[Repository](https://gitlab.torproject.org/tpo/applications/tor-browser-bundle-testsuite)
+
+It contains a test suite for Tor Browser.
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