Development with Custom GeckoView

If you are an engineer working on Gecko(View) then you might be interested in building Focus/Klar with your own build of GeckoView.

For this you will need to:

  • Checkout mozilla-central (or another branch)

  • Setup your system to build Firefox for Android

  • Package a GeckoView AAR

  • Modify your Focus gradle configuration to use your custom GeckoView AAR.

Setup build system

Follow the Build instructions to setup a Firefox for Android build (ARM or x86).

A minimal mozconfig for GeckoView development might look like this (ARM):

ac_add_options --enable-application=mobile/android
ac_add_options --target=arm-linux-androideabi
# For x86 use: ac_add_options --target=i386-linux-android

ac_add_options --with-android-sdk="<path-to-android-SDK>"
ac_add_options --with-android-ndk="<path-to-android-NDK>"

Package GeckoView AAR

After setting up your build system you should be able to build and package Firefox for Android:

./mach build
./mach package

Now you can create the GeckoView AAR from the compiled code:

./mach android archive-geckoview

This should create a file named geckoview-*.aar in your build output folder (MOZ_OBJDIR):

$ ls <your-output-directory>/gradle/build/mobile/android/geckoview/outputs/aar

Point your Focus/Klar build to your AAR

In your Focus/Klar checkout open app/build.gradle (not the build.gradle file in the root directory!) and locate the repositories block. This block defines where gradle will look for dependencies. Add the absolute path to your AAR as follows:

repositories {
    // ...

        name: 'localBuild',
        dirs: '<absolute path to AAR>'

Now locate the dependencies block. This block defines which dependencies are needed to compile the application. Locate the already existing armImplementation and x86Implementation statements. Those are currently pointing to AARs that are pulled from our build servers. Replace the correct one (x86 / ARM) to use the name of your local AAR:

dependencies {
    // ...

    // armImplementation "org.mozilla:geckoview-nightly-armeabi-v7a:60.0a1"
    armImplementation (
            name: 'geckoview-official-withGeckoBinaries-noMinApi-release',
            ext: 'aar'
    x86Implementation "org.mozilla:geckoview-nightly-x86:60.0a1"

    // ...

Now either build the klarArmDebug or klarX86Debug build variant from Android Studio (Running “Sync Project with Gradle files” once might be needed) or build and install from the command line:

./gradlew installKlarArmDebug
./gradlew installKlarX86Debug

Finally, the default renderer might be set as Webview. You can check for the presence or absence of the Gecko logo at focus:about to verify. You may change rendering engine settings at focus:test and then press back for the app to restart. This should store your engine preference until you uninstall or clear data.

You can also change the default engine at focus-android/app/src/debug/java/org/mozilla/focus/web/Config.kt. Setting DEFAULT_NEW_RENDERER to true will use GeckoView.