The Firefox for Android app has always had a complicated build process - we're cramping a complex cross-platform browser engine and all the related components that make it work on Android into one package. In its current form, it lives in the Firefox mono-repo at mozilla-central (now mozilla-firefox using the git repository).
I wanted to document my "artifact-mode" environment here since it's worked quite successfully for me for many years with minor changes.
NOTE: After a fresh clone of the mono-repo, don't forget to first run and follow the prompts of ./mach bootstrap .
mozconfig
My mozconfig below is enabled for artifact mode, but occasionally I switch between various configurations. You can see those commented out, with these few extra notes:
I like to separate out my objdirs to avoid cache pollution between the different build types. I think you can get away without needing to specify this and an objdir for your build type and arch will be generated.
sccache speeds up the native portion of full builds after the first slow one, but it's a hit or miss if you fetch from the remote repository but don't need to rebuild as often.
I don't care to manually run the clobber step, and I don't truly appreciate why that isn't always automatically done.
# Build GeckoView/Firefox for Android:
ac_add_options --enable-application=mobile/android
# Targeting the following architecture.
# For regular phones, no --target is needed.
# For x86 emulators (and x86 devices, which are uncommon):
# ac_add_options --target=i686
# For newer phones or Apple silicon
ac_add_options --target=aarch64
# For x86_64 emulators (and x86_64 devices, which are even less common):
# ac_add_options --target=x86_64
# sccache will significantly speed up your builds by caching
# compilation results. The Firefox build system will download
# sccache automatically.
# This only works for non-artifact builds.
#ac_add_options --with-ccache=sccache
# Enable artifact builds; manager-mode.
ac_add_options --enable-artifact-builds
# Write build artifacts to..
## Full build dir
#mk_add_options MOZ_OBJDIR=./objdir-droid
#mk_add_options MOZ_OBJDIR=./objdir-desktop
## Artifact builds
mk_add_options MOZ_OBJDIR=./objdir-frontend
# Automatic clobbering; don't ask me.
mk_add_options AUTOCLOBBER=1
JAVA_HOME
Sometimes you might find yourself needing to run a (non-mach) command in the terminal. Those typically will need to invoke some parts of gradle for an Android build, so it's best to make sure those are using the same JDK as the bootstrapped one in the mono-repo. This avoids weird build errors where something that compiles in one place isn't working in another (like Android Studio).
The location for the JDKs are typically in ~/.mozbuild/jdk/, and if you've between around for ~6 months you end up with multiple versions after every JDK bump:
$ ls -l ~/.mozbuild/jdk/
drwxr-xr-x@ - jalmeida 15 Apr 2025 jdk-17.0.15+6
drwxr-xr-x@ - jalmeida 15 Jul 2025 jdk-17.0.16+8
drwxr-xr-x@ - jalmeida 21 Oct 2025 jdk-17.0.17+10
drwxr-xr-x@ - jalmeida 20 Jan 09:00 jdk-17.0.18+8
drwxr-xr-x@ - jalmeida 26 Feb 15:04 mozboot
You can find some way to point your latest JDK to one location or you can be lazy like me and pick the latest version to assign as your JAVA_HOME property by adding this to your shell's RC file:
export JAVA_HOME="$(ls -1dr -- $HOME/.mozbuild/jdk/jdk-* | head -n 1)/Contents/Home"
Android Studio
UPDATE: With D286123 landed, this should no longer be necessary! 🎉
Similarly for Android Studio, let's do the same so that environment is identical. Head to, Settings | Build, Execution, Deployment | Build Tools | Gradle, and ensure that "Gradle JDK" path is set to JAVA_HOME.
Lately, the default seems to be for it to follow GRADLE_LOCAL_JAVA_HOME which is a property we can't easily override, so we have to manually set this ourselves.
Using the same Android SDK also helps speed things up and avoids source confusion. You can typically find it in ~/.mozbuild/android-sdk-macosx and update it at Settings | Languages & Frameworks | Android SDK.
Debugging
This section is for miscellaneous build error situations that come-up, but assuming mach build work and there are no known Android build changes, my solution has typically always been the same.
For example, the other day I fetched another engineers patch to test out locally1 as part of reviewing it where I faced the error message below:
Execution failed for task ':components:feature-pwa:compileDebugKotlin'.
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':components:feature-pwa:compileDebugKotlin'.
> A failure occurred while executing org.jetbrains.kotlin.compilerRunner.GradleCompilerRunnerWithWorkers$GradleKotlinCompilerWorkAction
> Internal compiler error. See log for more details
* Try:
> Run with --info or --debug option to get more log output.
> Run with --scan to generate a Build Scan (powered by Develocity).
> Get more help at https://help.gradle.org.
* Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':components:feature-pwa:compileDebugKotlin'.
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.lambda$executeIfValid$1(ExecuteActionsTaskExecuter.java:135)
at org.gradle.internal.Try$Failure.ifSuccessfulOrElse(Try.java:288)
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeIfValid(ExecuteActionsTaskExecuter.java:133)
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:121)
at org.gradle.api.internal.tasks.execution.ProblemsTaskPathTrackingTaskExecuter.execute(ProblemsTaskPathTrackingTaskExecuter.java:41)
at org.gradle.api.internal.tasks.execution.FinalizePropertiesTaskExecuter.execute(FinalizePropertiesTaskExecuter.java:46)
at org.gradle.api.internal.tasks.execution.ResolveTaskExecutionModeExecuter.execute(ResolveTaskExecutionModeExecuter.java:51)
at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:57)
at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:74)
at org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:36)
at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.executeTask(EventFiringTaskExecuter.java:77)
at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.call(EventFiringTaskExecuter.java:55)
at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.call(EventFiringTaskExecuter.java:52)
at org.gradle.internal.operations.DefaultBuildOperationRunner$CallableBuildOperationWorker.execute(DefaultBuildOperationRunner.java:209)
at org.gradle.internal.operations.DefaultBuildOperationRunner$CallableBuildOperationWorker.execute(DefaultBuildOperationRunner.java:204)
at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:66)
at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:59)
at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:166)
at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:59)
at org.gradle.internal.operations.DefaultBuildOperationRunner.call(DefaultBuildOperationRunner.java:53)
at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter.execute(EventFiringTaskExecuter.java:52)
at org.gradle.execution.plan.DefaultNodeExecutor.executeLocalTaskNode(DefaultNodeExecutor.java:55)
at org.gradle.execution.plan.DefaultNodeExecutor.execute(DefaultNodeExecutor.java:34)
at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:355)
at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:343)
at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.lambda$execute$0(DefaultTaskExecutionGraph.java:339)
at org.gradle.internal.operations.CurrentBuildOperationRef.with(CurrentBuildOperationRef.java:84)
at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:339)
at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:328)
at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.execute(DefaultPlanExecutor.java:459)
at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.run(DefaultPlanExecutor.java:376)
at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:64)
at org.gradle.internal.concurrent.AbstractManagedExecutor$1.run(AbstractManagedExecutor.java:47)
Caused by: org.gradle.workers.internal.DefaultWorkerExecutor$WorkExecutionException: A failure occurred while executing org.jetbrains.kotlin.compilerRunner.GradleCompilerRunnerWithWorkers$GradleKotlinCompilerWorkAction
at org.gradle.workers.internal.DefaultWorkerExecutor$WorkItemExecution.waitForCompletion(DefaultWorkerExecutor.java:289)
at org.gradle.internal.work.DefaultAsyncWorkTracker.lambda$waitForItemsAndGatherFailures$2(DefaultAsyncWorkTracker.java:130)
at org.gradle.internal.Factories$1.create(Factories.java:33)
at org.gradle.internal.work.DefaultWorkerLeaseService.lambda$withoutLocks$2(DefaultWorkerLeaseService.java:344)
at org.gradle.internal.work.ResourceLockStatistics$1.measure(ResourceLockStatistics.java:42)
at org.gradle.internal.work.DefaultWorkerLeaseService.withoutLocks(DefaultWorkerLeaseService.java:342)
at org.gradle.internal.work.DefaultWorkerLeaseService.withoutLocks(DefaultWorkerLeaseService.java:326)
at org.gradle.internal.work.DefaultWorkerLeaseService.withoutLock(DefaultWorkerLeaseService.java:331)
at org.gradle.internal.work.DefaultAsyncWorkTracker.waitForItemsAndGatherFailures(DefaultAsyncWorkTracker.java:126)
at org.gradle.internal.work.DefaultAsyncWorkTracker.waitForItemsAndGatherFailures(DefaultAsyncWorkTracker.java:92)
at org.gradle.internal.work.DefaultAsyncWorkTracker.waitForAll(DefaultAsyncWorkTracker.java:78)
at org.gradle.internal.work.DefaultAsyncWorkTracker.waitForCompletion(DefaultAsyncWorkTracker.java:66)
at org.gradle.api.internal.tasks.execution.TaskExecution$3.run(TaskExecution.java:260)
at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:29)
at org.gradle.internal.operations.DefaultBuildOperationRunner$1.execute(DefaultBuildOperationRunner.java:26)
at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:66)
at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:59)
at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:166)
at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:59)
at org.gradle.internal.operations.DefaultBuildOperationRunner.run(DefaultBuildOperationRunner.java:47)
at org.gradle.api.internal.tasks.execution.TaskExecution.executeAction(TaskExecution.java:237)
at org.gradle.api.internal.tasks.execution.TaskExecution.executeActions(TaskExecution.java:220)
at org.gradle.api.internal.tasks.execution.TaskExecution.executeWithPreviousOutputFiles(TaskExecution.java:203)
at org.gradle.api.internal.tasks.execution.TaskExecution.execute(TaskExecution.java:170)
at org.gradle.internal.execution.steps.ExecuteStep.executeInternal(ExecuteStep.java:105)
at org.gradle.internal.execution.steps.ExecuteStep.access$000(ExecuteStep.java:44)
at org.gradle.internal.execution.steps.ExecuteStep$1.call(ExecuteStep.java:59)
at org.gradle.internal.execution.steps.ExecuteStep$1.call(ExecuteStep.java:56)
at org.gradle.internal.operations.DefaultBuildOperationRunner$CallableBuildOperationWorker.execute(DefaultBuildOperationRunner.java:209)
at org.gradle.internal.operations.DefaultBuildOperationRunner$CallableBuildOperationWorker.execute(DefaultBuildOperationRunner.java:204)
at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:66)
at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:59)
at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:166)
at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:59)
at org.gradle.internal.operations.DefaultBuildOperationRunner.call(DefaultBuildOperationRunner.java:53)
at org.gradle.internal.execution.steps.ExecuteStep.execute(ExecuteStep.java:56)
at org.gradle.internal.execution.steps.ExecuteStep.execute(ExecuteStep.java:44)
at org.gradle.internal.execution.steps.CancelExecutionStep.execute(CancelExecutionStep.java:42)
at org.gradle.internal.execution.steps.TimeoutStep.executeWithoutTimeout(TimeoutStep.java:75)
at org.gradle.internal.execution.steps.TimeoutStep.execute(TimeoutStep.java:55)
at org.gradle.internal.execution.steps.PreCreateOutputParentsStep.execute(PreCreateOutputParentsStep.java:50)
at org.gradle.internal.execution.steps.PreCreateOutputParentsStep.execute(PreCreateOutputParentsStep.java:28)
at org.gradle.internal.execution.steps.RemovePreviousOutputsStep.execute(RemovePreviousOutputsStep.java:68)
at org.gradle.internal.execution.steps.RemovePreviousOutputsStep.execute(RemovePreviousOutputsStep.java:38)
at org.gradle.internal.execution.steps.BroadcastChangingOutputsStep.execute(BroadcastChangingOutputsStep.java:61)
at org.gradle.internal.execution.steps.BroadcastChangingOutputsStep.execute(BroadcastChangingOutputsStep.java:26)
at org.gradle.internal.execution.steps.CaptureOutputsAfterExecutionStep.execute(CaptureOutputsAfterExecutionStep.java:69)
at org.gradle.internal.execution.steps.CaptureOutputsAfterExecutionStep.execute(CaptureOutputsAfterExecutionStep.java:46)
at org.gradle.internal.execution.steps.ResolveInputChangesStep.execute(ResolveInputChangesStep.java:39)
at org.gradle.internal.execution.steps.ResolveInputChangesStep.execute(ResolveInputChangesStep.java:28)
at org.gradle.internal.execution.steps.BuildCacheStep.executeWithoutCache(BuildCacheStep.java:189)
at org.gradle.internal.execution.steps.BuildCacheStep.lambda$execute$1(BuildCacheStep.java:75)
at org.gradle.internal.Either$Right.fold(Either.java:176)
at org.gradle.internal.execution.caching.CachingState.fold(CachingState.java:62)
at org.gradle.internal.execution.steps.BuildCacheStep.execute(BuildCacheStep.java:73)
at org.gradle.internal.execution.steps.BuildCacheStep.execute(BuildCacheStep.java:48)
at org.gradle.internal.execution.steps.StoreExecutionStateStep.execute(StoreExecutionStateStep.java:46)
at org.gradle.internal.execution.steps.StoreExecutionStateStep.execute(StoreExecutionStateStep.java:35)
at org.gradle.internal.execution.steps.SkipUpToDateStep.executeBecause(SkipUpToDateStep.java:75)
at org.gradle.internal.execution.steps.SkipUpToDateStep.lambda$execute$2(SkipUpToDateStep.java:53)
at org.gradle.internal.execution.steps.SkipUpToDateStep.execute(SkipUpToDateStep.java:53)
at org.gradle.internal.execution.steps.SkipUpToDateStep.execute(SkipUpToDateStep.java:35)
at org.gradle.internal.execution.steps.legacy.MarkSnapshottingInputsFinishedStep.execute(MarkSnapshottingInputsFinishedStep.java:37)
at org.gradle.internal.execution.steps.legacy.MarkSnapshottingInputsFinishedStep.execute(MarkSnapshottingInputsFinishedStep.java:27)
at org.gradle.internal.execution.steps.ResolveIncrementalCachingStateStep.executeDelegate(ResolveIncrementalCachingStateStep.java:49)
at org.gradle.internal.execution.steps.ResolveIncrementalCachingStateStep.executeDelegate(ResolveIncrementalCachingStateStep.java:27)
at org.gradle.internal.execution.steps.AbstractResolveCachingStateStep.execute(AbstractResolveCachingStateStep.java:71)
at org.gradle.internal.execution.steps.AbstractResolveCachingStateStep.execute(AbstractResolveCachingStateStep.java:39)
at org.gradle.internal.execution.steps.ResolveChangesStep.execute(ResolveChangesStep.java:64)
at org.gradle.internal.execution.steps.ResolveChangesStep.execute(ResolveChangesStep.java:35)
at org.gradle.internal.execution.steps.ValidateStep.execute(ValidateStep.java:62)
at org.gradle.internal.execution.steps.ValidateStep.execute(ValidateStep.java:40)
at org.gradle.internal.execution.steps.AbstractCaptureStateBeforeExecutionStep.execute(AbstractCaptureStateBeforeExecutionStep.java:76)
at org.gradle.internal.execution.steps.AbstractCaptureStateBeforeExecutionStep.execute(AbstractCaptureStateBeforeExecutionStep.java:45)
at org.gradle.internal.execution.steps.AbstractSkipEmptyWorkStep.executeWithNonEmptySources(AbstractSkipEmptyWorkStep.java:136)
at org.gradle.internal.execution.steps.AbstractSkipEmptyWorkStep.execute(AbstractSkipEmptyWorkStep.java:66)
at org.gradle.internal.execution.steps.AbstractSkipEmptyWorkStep.execute(AbstractSkipEmptyWorkStep.java:38)
at org.gradle.internal.execution.steps.legacy.MarkSnapshottingInputsStartedStep.execute(MarkSnapshottingInputsStartedStep.java:38)
at org.gradle.internal.execution.steps.LoadPreviousExecutionStateStep.execute(LoadPreviousExecutionStateStep.java:36)
at org.gradle.internal.execution.steps.LoadPreviousExecutionStateStep.execute(LoadPreviousExecutionStateStep.java:23)
at org.gradle.internal.execution.steps.HandleStaleOutputsStep.execute(HandleStaleOutputsStep.java:75)
at org.gradle.internal.execution.steps.HandleStaleOutputsStep.execute(HandleStaleOutputsStep.java:41)
at org.gradle.internal.execution.steps.AssignMutableWorkspaceStep.lambda$execute$0(AssignMutableWorkspaceStep.java:35)
at org.gradle.api.internal.tasks.execution.TaskExecution$4.withWorkspace(TaskExecution.java:297)
at org.gradle.internal.execution.steps.AssignMutableWorkspaceStep.execute(AssignMutableWorkspaceStep.java:31)
at org.gradle.internal.execution.steps.AssignMutableWorkspaceStep.execute(AssignMutableWorkspaceStep.java:22)
at org.gradle.internal.execution.steps.ChoosePipelineStep.execute(ChoosePipelineStep.java:40)
at org.gradle.internal.execution.steps.ChoosePipelineStep.execute(ChoosePipelineStep.java:23)
at org.gradle.internal.execution.steps.ExecuteWorkBuildOperationFiringStep.lambda$execute$2(ExecuteWorkBuildOperationFiringStep.java:67)
at org.gradle.internal.execution.steps.ExecuteWorkBuildOperationFiringStep.execute(ExecuteWorkBuildOperationFiringStep.java:67)
at org.gradle.internal.execution.steps.ExecuteWorkBuildOperationFiringStep.execute(ExecuteWorkBuildOperationFiringStep.java:39)
at org.gradle.internal.execution.steps.IdentityCacheStep.execute(IdentityCacheStep.java:46)
at org.gradle.internal.execution.steps.IdentityCacheStep.execute(IdentityCacheStep.java:34)
at org.gradle.internal.execution.steps.IdentifyStep.execute(IdentifyStep.java:44)
at org.gradle.internal.execution.steps.IdentifyStep.execute(IdentifyStep.java:31)
at org.gradle.internal.execution.impl.DefaultExecutionEngine$1.execute(DefaultExecutionEngine.java:64)
at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeIfValid(ExecuteActionsTaskExecuter.java:132)
... 30 more
Caused by: org.jetbrains.kotlin.gradle.tasks.FailedCompilationException: Internal compiler error. See log for more details
at org.jetbrains.kotlin.gradle.tasks.TasksUtilsKt.throwExceptionIfCompilationFailed(tasksUtils.kt:22)
at org.jetbrains.kotlin.compilerRunner.GradleKotlinCompilerWork.run(GradleKotlinCompilerWork.kt:112)
at org.jetbrains.kotlin.compilerRunner.GradleCompilerRunnerWithWorkers$GradleKotlinCompilerWorkAction.execute(GradleCompilerRunnerWithWorkers.kt:75)
at org.gradle.workers.internal.DefaultWorkerServer.execute(DefaultWorkerServer.java:68)
at org.gradle.workers.internal.NoIsolationWorkerFactory$1$1.create(NoIsolationWorkerFactory.java:64)
at org.gradle.workers.internal.NoIsolationWorkerFactory$1$1.create(NoIsolationWorkerFactory.java:61)
at org.gradle.internal.classloader.ClassLoaderUtils.executeInClassloader(ClassLoaderUtils.java:100)
at org.gradle.workers.internal.NoIsolationWorkerFactory$1.lambda$execute$0(NoIsolationWorkerFactory.java:61)
at org.gradle.workers.internal.AbstractWorker$1.call(AbstractWorker.java:44)
at org.gradle.workers.internal.AbstractWorker$1.call(AbstractWorker.java:41)
at org.gradle.internal.operations.DefaultBuildOperationRunner$CallableBuildOperationWorker.execute(DefaultBuildOperationRunner.java:209)
at org.gradle.internal.operations.DefaultBuildOperationRunner$CallableBuildOperationWorker.execute(DefaultBuildOperationRunner.java:204)
at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:66)
at org.gradle.internal.operations.DefaultBuildOperationRunner$2.execute(DefaultBuildOperationRunner.java:59)
at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:166)
at org.gradle.internal.operations.DefaultBuildOperationRunner.execute(DefaultBuildOperationRunner.java:59)
at org.gradle.internal.operations.DefaultBuildOperationRunner.call(DefaultBuildOperationRunner.java:53)
at org.gradle.workers.internal.AbstractWorker.executeWrappedInBuildOperation(AbstractWorker.java:41)
at org.gradle.workers.internal.NoIsolationWorkerFactory$1.execute(NoIsolationWorkerFactory.java:58)
at org.gradle.workers.internal.DefaultWorkerExecutor.lambda$submitWork$0(DefaultWorkerExecutor.java:176)
at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.runExecution(DefaultConditionalExecutionQueue.java:194)
at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.access$700(DefaultConditionalExecutionQueue.java:127)
at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner$1.run(DefaultConditionalExecutionQueue.java:169)
at org.gradle.internal.Factories$1.create(Factories.java:33)
at org.gradle.internal.work.DefaultWorkerLeaseService.lambda$withLocksAcquired$0(DefaultWorkerLeaseService.java:269)
at org.gradle.internal.work.ResourceLockStatistics$1.measure(ResourceLockStatistics.java:42)
at org.gradle.internal.work.DefaultWorkerLeaseService.withLocksAcquired(DefaultWorkerLeaseService.java:267)
at org.gradle.internal.work.DefaultWorkerLeaseService.withLocks(DefaultWorkerLeaseService.java:259)
at org.gradle.internal.work.DefaultWorkerLeaseService.runAsWorkerThread(DefaultWorkerLeaseService.java:127)
at org.gradle.internal.work.DefaultWorkerLeaseService.runAsWorkerThread(DefaultWorkerLeaseService.java:132)
at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.runBatch(DefaultConditionalExecutionQueue.java:164)
at org.gradle.internal.work.DefaultConditionalExecutionQueue$ExecutionRunner.run(DefaultConditionalExecutionQueue.java:133)
... 2 more
The full trace was long and didn't seem related to a code failure in the module itself. So I employed the solution, which is always the same:
./mach build
In Android Studio, File > Sync Project with Gradle Files.
Yup, that's all. Very simple and boring.
1
With Jujutsu, this is the moz-phab command I use which has made it easier to manage review patches: moz-phab patch <patch-id> --no-branch --apply-to main@origin
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Update on May 19, 2026: Firefox's free built-in VPN now supports location selection, giving people access to a fully comprehensive VPN experience directly within the browser. Starting today, Firefox users in the U.S., U.K., France, Germany, and Canada can choose to browse from any of the countries where we've launched VPN support. Browsing is subject to the local laws and content restrictions of the selected region.
Original post from March 2026:
Today we're introducing a free built-in VPN in Firefox, a new IP-protection feature designed to keep you even more private while you browse. We're starting by offering an industry-leading 50 gigabytes of free VPN-browsing each month.
Firefox has long focused on building privacy tools directly into the browser to protect you online. Over the years, we've introduced world-class protections that block known trackers, reduce fingerprinting and limit how companies can follow people across the web. Our goal has been consistent: make meaningful privacy protections accessible to Firefox users every day.
Firefox is the only major browser to include a built-in VPN like this for free - giving you more control over your privacy, right where you browse.
Privacy built into the browser
Every time you visit a website, your IP address is shared automatically. IP addresses help websites know where to send information back to your device, but they can also be used to approximate your location, link your browsing activity across sites and keep logs about your online behavior, meaning websites can track your behavior. It's one of many ways companies track activity across the internet.
Additionally, when you're using public Wi-Fi while at a coffee shop, in a hotel, or in your dorm, people can spy on your network traffic and see which websites you might be visiting.
At Mozilla, we believe people should have stronger protections against this kind of tracking and spying, and that those protections should be easy to use.
Introducing built-in VPN
Our free built-in VPN is designed to make IP protection simple to use in Firefox.
The built-in VPN includes an unprecedented 50 GB per month of free VPN browsing, enough to cover everyday activities like shopping, banking, and reading.
Turn it on in Firefox with a single click. No extra apps. No downloads. Once it's on, Firefox routes your browsing traffic through a proxy network that replaces your IP address before it reaches a website. The sites you visit see the proxy's IP address rather than your own. Firefox already encrypts your traffic with HTTPS, but masking your IP adds another layer of privacy. You can mask the URLs you're visiting from anyone trying to spy on your network traffic on public Wi-Fi, like while you're enjoying a latte at your favorite coffee shop.
If you reach the monthly limit, IP protection is paused until the next cycle. Firefox will require you to confirm before proceeding without the VPN so your browsing doesn't unintentionally continue without IP protection.
Browser-level protection and full-device protection
The free built-in VPN helps secure your traffic while browsing in Firefox, making it a simple way to protect your IP address from being tracked by big tech. However, it does not offer full device protection.
For those looking for broader coverage, you can also choose protection that extends across your entire device, including other apps. The standalone Mozilla VPN subscription offers this capability with unlimited data across multiple devices. Depending on your needs, you can pick the level of privacy and protection that suits you.
We've heard concerns about so-called "free VPNs," which often rely on advertising or selling user data to generate revenue. Firefox's built-in VPN is designed differently. It does not sell your browsing data and does not inject advertising into your traffic. Instead, we offer a limited amount of browser-level protection for free, alongside Mozilla VPN, our paid, unlimited, full-device VPN service.
The free built-in VPN is currently rolling out as a beta to Firefox desktop users in the United States, the United Kingdom, Germany and France, with plans to expand to additional countries coming soon over the next several releases.
As with many Firefox features, we're introducing it gradually starting in Firefox 149 so we can learn from user feedback and continue improving the experience.
Building a more private web
Protecting privacy online is an ongoing effort. As the web evolves, new technologies create both opportunities and challenges for keeping personal information safe.
Mozilla has spent years building privacy protections - from Total Cookie Protection to Private browsing mode to anti-fingerprinting - directly into Firefox so people have more control over how they experience the web. This built-in VPN is one more way Firefox helps you browse with less exposure and more peace of mind.
By continuing to build these protections into Firefox, we aim to make the web safer, more transparent and more respectful of the people who use it.
Today, Firefox is rolling out updates across desktop and mobile that give you more choice over how you browse.
Here's a look at what's new.
Adding location selection to Firefox's free VPN
Firefox now offers a fully featured VPN experience directly in the browser - for free. In just two months, over 1 million users have already signed up to try it.
With the addition of location selection, one of the most requested features from the Firefox community, Firefox's free built-in VPN now delivers all the flexibility and functionality people expect from a modern VPN.
Starting today, Firefox users in the U.S., U.K., France, Germany, and Canada can choose to browse from any of the countries where we've launched VPN support. Whether you want to view local news, shop regionally, or see how content appears in another country, location selection gives you more control over where your connection appears from online.
Firefox will recommend the location closest to you by default, but people can switch locations at any time. Additional locations are planned for future releases. Browsing will still be subject to the local laws and content restrictions of the selected region.
Available in Firefox 151.
More controls over AI features on mobile
You can now decide how AI shows up in your Firefox mobile browsing experience, with more control over which AI features to activate and more ways to use them across devices and languages.
After launching AI controls on desktop earlier this year, Firefox is bringing them to iOS and Android. Depending on your device and region, available controls include features like translations, voice search and Shake to Summarize. Preferences can be updated at any time, making it easy to keep only the tools you want to use as new AI-powered features arrive in Firefox.
Shake to Summarize, recognized by TIME as one of the Best Inventions of 2025, helps you cut to the chase on mobile webpages by generating a simple summary with a flick of your wrist. The feature is now expanding to Android devices, with English rolling out first and additional languages coming soon. Shake to Summarize is now available on iOS in English, German, French, Spanish, Portuguese, Italian, and Japanese, giving more people the option to use it in the language that works best for them.
AI controls are available on iOS and Android. Shake to Summarize is available on Android in English and on iOS in English, German, French, Spanish, Portuguese, Italian, and Japanese.
A one-click reset for Private Browsing
Finished shopping for a surprise gift or logging into a temporary account? A new flame-shaped "Clear Private Session" button, located to the right of the address bar, instantly clears your current private session and starts a new one without requiring you to close and reopen the browser. Cookies, browsing history, logins, and other session data from your private windows are deleted automatically. Read more in this week's release notes.
Try it out in Firefox 151.
Coming soon in Nightly: A refreshed settings page
Firefox is previewing a redesigned settings page in Nightly that makes it easier to find the controls you're looking for and move through settings more intuitively. The redesign introduces improved navigation, clearer organization, and updated labels and descriptions designed to make customization easier.
Existing settings and preferences will remain unchanged, and the updated search experience helps people quickly find settings that may appear in new sections.
This will be enabled by default for Nightly users starting later this week.
Download the latest version of Firefox to explore what's new and share feedback with us on Mozilla Connect.
