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Android components

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A collection of Android libraries to build browsers or browser-like applications.

ℹ️ For more information see the website.

A fully-featured reference browser implementation based on the components can be found in the reference-browser repository.

Getting Involved

We encourage you to participate in this open source project. We love pull requests, bug reports, ideas, (security) code reviews or any kind of positive contribution.

Before you attempt to make a contribution please read the Community Participation Guidelines.

Maven repository

All components are getting published on To use them, you need to add the following to your project's top-level build file, in the allprojects block (see e.g. the reference-browser):

repositories {
    maven {
       url ""

Each module that uses a component needs to specify it in its build file, in the dependencies block. For example, to use the Base component (in the support) collection, you need:

dependencies {
    implementation 'org.mozilla.components:support-base:+'

Nightly builds

Nightly builds are created every day from the main branch and published on


  • 🔴 In Development - Not ready to be used in shipping products.
  • Preview - This component is almost/partially ready and can be tested in products.
  • 🔵 Production ready - Used by shipping products.


High-level components for building browser(-like) apps.

  • 🔵 Awesomebar - A customizable Awesome Bar implementation for browsers.

  • 🔵 Domains Localized and customizable domain lists for auto-completion in browsers.

  • 🔵 Engine-Gecko - Engine implementation based on GeckoView.

  • 🔵 Engine-System - Engine implementation based on the system's WebView.

  • 🔵 Errorpages - Responsive browser error pages for Android apps.

  • 🔵 Icons - A component for loading and storing website icons (like Favicons).

  • 🔵 Menu - A generic menu with customizable items primarily for browser toolbars.

  • Menu 2 - A generic menu with customizable items primarily for browser toolbars.

  • 🔵 Session-Storage - Component for saving and restoring the browser state.

  • 🔵 State - Component for maintaining the centralized state of the browser and its components.

  • 🔵 Storage-Sync - A syncable implementation of browser storage backed by application-services' Places lib.

  • 🔵 Tabstray - A customizable tabs tray for browsers.

  • 🔵 Thumbnails - A component for loading and storing website thumbnails (screenshot of the website).

  • 🔵 Toolbar - A customizable toolbar for browsers.


API contracts and abstraction layers for browser components.

  • 🔵 Awesomebar - An abstract definition of an awesome bar component.

  • 🔵 Engine - Abstraction layer that allows hiding the actual browser engine implementation.

  • 🔵 Fetch - An abstract definition of an HTTP client for fetching resources.

  • 🔵 Push - An abstract definition of a push service component.

  • 🔵 Storage - Abstract definition of a browser storage component.

  • 🔵 Tabstray - Abstract definition of a tabs tray component.

  • 🔵 Toolbar - Abstract definition of a browser toolbar component.


Combined components to implement feature-specific use cases.

  • 🔵 Accounts - A component that connects an FxaAccountManager from service-firefox-accounts with feature-tabs in order to facilitate authentication flows.

  • 🔵 Accounts Push - Feature of use cases for FxA Account that work with push support.

  • 🔵 Autofill - A component that provides support for Android's Autofill framework.

  • 🔵 Awesomebar - A component that connects a concept-awesomebar implementation to a concept-toolbar implementation and provides implementations of various suggestion providers.

  • 🔴 Containers - A component for working with contextual identities also known as containers.

  • 🔵 Context Menu - A component for displaying context menus when long-pressing web content.

  • 🔵 Custom Tabs - A component for providing Custom Tabs functionality in browsers.

  • 🔵 Downloads - A component to perform downloads using the Android downloads manager.

  • 🔵 Intent - A component that provides intent processing functionality by combining various other feature modules.

  • Progressive Web Apps (PWA) - A component that provides functionality for supporting Progressive Web Apps (PWA).

  • 🔵 Reader View - A component that provides Reader View functionality.

  • 🔵 QR - A component that provides functionality for scanning QR codes.

  • 🔵 Search - A component that connects an (concept) engine implementation with the browser search module.

  • 🔵 Session - A component that connects an (concept) engine implementation with the browser session and storage modules.

  • 🔵 Share - Feature implementation for saving and sorting recent apps used for sharing.

  • 🔵 Sync -A component that provides synchronization orchestration for groups of (concept) SyncableStore objects.

  • 🔵 Tabs - A component that connects a tabs tray implementation with the session and toolbar modules.

  • 🔵 Tab Collections - Feature implementation for saving, restoring and organizing collections of tabs.

  • 🔵 Toolbar - A component that connects a (concept) toolbar implementation with the browser session module.

  • 🔵 Top Sites - Feature implementation for saving and removing top sites.

  • 🔵 Prompts - A component that will handle all the common prompt dialogs from web content.

  • 🔵 Push - A component that provides Autopush messages with help from a supported push service.

  • 🔵 Find In Page - A component that provides an UI widget for find in page functionality.

  • 🔵 Remote Tabs - Feature that provides access to other device's tabs in the same account.

  • 🔵 Site Permissions - A feature for showing site permission request prompts.

  • 🔵 WebAuthn - A feature that provides WebAuthn functionality for supported engines.

  • 🔵 Web Notifications - A component for displaying web notifications.

  • 🔵 WebCompat - A feature to enable website-hotfixing via the Web Compatibility System-Addon.

  • 🔵 WebCompat Reporter - A feature that enables users to report site issues to Mozilla's Web Compatibility team for further diagnosis.

  • 🔵 Web Add-ons - A feature that provides functionality for managing add-ons.


Generic low-level UI components for building apps.

  • 🔵 Autocomplete - A set of components to provide autocomplete functionality.

  • 🔵 Colors - The standard set of Photon colors.

  • 🔵 Fonts - The standard set of fonts used by Mozilla Android products.

  • 🔵 Icons - A collection of often used browser icons.

  • 🔵 Tabcounter - A button that shows the current tab count and can animate state changes.


Components and libraries to interact with backend services.

  • 🔵 Firefox Accounts (FxA) - A library for integrating with Firefox Accounts.

  • 🔵 Firefox Sync - Logins - A library for integrating with Firefox Sync - Logins.

  • 🔵 Firefox Sync - Autofill - A library for integrating with Firefox Sync - Autofill.

  • 🔵 Glean - A client-side telemetry SDK for collecting metrics and sending them to Mozilla's telemetry service (eventually replacing service-telemetry).

  • 🔵 Location - A library for accessing Mozilla's and other location services.

  • 🔴 Nimbus - A wrapper for the Nimbus SDK.

  • 🔵 Pocket - A library for communicating with the Pocket API.

  • 🔵 Contile - A library for communicating with the Contile services API.


Supporting components with generic helper code.

  • 🔵 Android Test - A collection of helpers for testing components in instrumented (on device) tests (src/androidTest).

  • 🔵 Base - Base component containing building blocks for components.

  • 🔵 Ktx - A set of Kotlin extensions on top of the Android framework and Kotlin standard library.

  • 🔵 Test - A collection of helpers for testing components in local unit tests (src/test).

  • 🔵 Test Appservices - A component for synchronizing Application Services' unit testing dependencies used in Android Components.

  • 🔵 Test LibState - A collection of helpers for testing functionality that relies on the lib-state component in local unit tests (src/test).

  • 🔵 Utils - Generic utility classes to be shared between projects.

  • 🔵 Webextensions - A component containing building blocks for features implemented as web extensions.

Standalone libraries


  • 🔵 Fetch-Tests - A generic test suite for components that implement concept-fetch.

  • 🔵 Lint - Custom Lint rules for the components repository.

Sample apps

Sample apps using various components.

  • Browser - A simple browser composed from browser components. This sample application is only a very basic browser. For a full-featured reference browser implementation see the reference-browser repository.

  • Crash - An app showing the integration of the lib-crash component.

  • Firefox Accounts (FxA) - A simple app demoing Firefox Accounts integration.

  • Firefox Sync - A simple app demoing general Firefox Sync integration, with bookmarks and history.

  • Firefox Sync - Logins - A simple app demoing Firefox Sync (Logins) integration.

  • DataProtect - An app demoing how to use the Dataprotect component to load and store encrypted data in SharedPreferences.

  • Glean - An app demoing how to use the Glean library to collect and send telemetry data.

  • Toolbar - An app demoing multiple customized toolbars using the browser-toolbar component.


Command line

$ git clone
$ cd android-components
$ ./gradlew assemble

Android Studio

If the environment variable JAVA_HOME is not defined, you will need to set it. If you would like to use the JDK installed by Android Studio, here's how to find it:

  1. Open Android Studio.
  2. Select "Configure".
  3. Select "Default Project Structure". You should now see the Android JDK location.
  4. Set the environment variable JAVA_HOME to the location. (How you set an environment variable depends on your OS.)
  5. Restart Android Studio.

Once the environment variable is set, you can import the project into Android Studio with the default wizard options.

If your build fails, you may find you get more instructive error messages by attempting the build at the command line.

Coding Standards


We follow the style enforced by ktlint and detekt. See how to configure Android Studio appropriately.

To check your style, run:

./gradlew ktlint
./gradlew detekt


We use files for each component.

If you fix a bug or change an API, you should update docs/


You are expected to both add tests for code that you write and make sure that your changes do not cause existing tests to fail. You may find these command lines helpful:

./gradlew test                             # Run all tests
./gradlew :support-ktx:testdebugunittest   # Run unit tests for a specified module

See also how to measure code coverage.


If your code has user-facing changes, follow Android accessibility best practices.


This Source Code Form is subject to the terms of the Mozilla Public
License, v. 2.0. If a copy of the MPL was not distributed with this
file, You can obtain one at