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Building Fennec

Right now it is possible to build Fennec on most UNIX-like systems, including Mac OS X and many flavors of Linux. Most core developers run Mac OS X; a handful run Linux.

Sadly we do not yet support building Fennec on Microsoft Windows. We know of no strong reason that it should not be possible (now; in the past, it was not possible because Google did not release certain parts of the Android toolchain for Windows), but it's also not a priority. If you're interested in building on Windows, or can contribute, please CC yourself onto bug 1169873.

Preparing your build environment

Run either of the following in a terminal. If you have curl installed (note that Mac OS X ships curl by default):

curl -O && python

If you have wget installed:

wget -q && python

Alternatively, if you already have a clone of the source code, you can also run

mach bootstrap

to run the setup script.

Choose to build "Firefox for Android" at the prompts. This will help you install all the build prerequisites required for building Fennec on the most popular host operating systems (including OS X and Debian-flavoured Linuxes, including Ubuntu; but sadly not including Windows).

You may need an hour or more to download and install prerequisites (Java, the Android SDK and NDK, and the Android platform itself, are very large). You may be prompted to enter your password or to accept license agreements.

NOTE: If that doesn't work, or you need more details: Follow the detailed instructions to set up a build environment on your machine. Once you have done that, follow the steps to get the source, set up your mozconfig, and build Fennec.

Getting the source

First, grab a clone of the Fennec source code repository:

hg clone

The source files will be in the mozilla-central directory, which we refer to as your source directory.

Before doing anything else, it's a good idea to install and configure Mercurial as described here.

Preparing a Fennec mozconfig

Next, navigate to your source directory and create a text file called "mozconfig". The mozconfig file is what tells the Mozilla build system what to build and how your build environment is prepared. Here is the minimal mozconfig file for building Fennec; it should be named mozconfig in your source directory, as the build scripts will read from the mozconfig file in your source directory by default, although you can configure this if you need to.

# Build Firefox for Android:
ac_add_options --enable-application=mobile/android
ac_add_options --target=arm-linux-androideabi

# With the following Android SDK and NDK:
ac_add_options --with-android-sdk="/path/to/android-sdk/platforms/android-22"
ac_add_options --with-android-ndk="/path/to/android-ndk-r10e"

This assumes you have followed the instructions above and are using Android platform 22 and NDK version r10e. You must use $HOME instead of ~ in your mozconfig because ~ does not get expanded.

Mozilla's build system writes all build intermediate files and output artifacts into a separate directory called the object directory. The build system will choose a reasonable default name for the object directory if you don't specify one, but it's common to specify an object directory starting with "obj" and to put it inside your source directory. Add a line like the following to your mozconfig:

mk_add_options MOZ_OBJDIR=./objdir-droid

Building and deploying the Fennec Android package

Before you start building, connect your Android device and enable USB debugging.

The following steps will build Fennec (compile and link all C/C++, Java, and JavaScript source code), prepare a fresh Fennec APK, and deploy Fennec to your Android device:

./mach build
./mach package
./mach install

The APK file can be found in your objdir-droid/dist folder, and will be called something like You can install this APK to your device manually using adb install or ./mach install.

The name of the app that shows up on your phone will be "Fennec $USER" (where $USER is the username under which you built the code).

To speed up subsequent builds you should build only part of the mobile/android directory using ./mach build mobile/android or ./mach build mobile/android/base, depending on where your changes are.

Mercurial and Workflow

Historically, Mozilla has used Mercurial patch queues to submit code changes for review. However, Mozilla developers are now encouraged to use a Mercurial bookmark-based workflow.

If you're a contributor and new to Mercurial, patch queues are conceptually simple and fine for getting your first few patches up; see the instructions on Mercurial patch queues.

If you're interested in using bookmarks, take a look at bookmarks-based development.

(If you want more information about bookmarks-based workflow, take a look at gps's slides; gps's blog is another good place to get information about version control at Mozilla.)

For more information about configuring your hg environment to work well at Mozilla, see Mercurial for Mozillians. Also, if you're curious to see an active hgrc with potentially useful aliases (and thus commonly used commands), check here.


We provide some support for linting tools. See Mobile/Fennec/Android/Lint for a list of linting tools we support and expect to be run.

Creating commits and submitting patches

Mercurial (hg) is the the main version control system that Mozilla uses, and to submit code for review, you should be able to generate patches or commits. Be sure to run mach mercurial-setup when cloning the source code repository -- this will ensure you have good default settings and extensions.

Instructions for submitting a patch can be found here. If you have already applied for level 1 commit access, be sure to check out MozReview.

After writing the patch, make sure the commit message is of the correct format:
Bug <bug#> - <bug title>. r=<reviewer>

So for example, for bug 1128431, the commit message should be:
Bug 1128431 - 'Start browsing' link from onboarding v1.5 is not visible on small screen devices. r=liuche

Android NDK and SDK version notes

Members of the Fennec community are successfully building Fennec with:

  • Android SDK Platform Android 5.1.1 (API 22)
  • SDK Build Tools 22.0.1
  • SDK Platform Tools 22
  • Android SDK Tools 24.3
  • Android Support Repository 15
  • Android Support Library 22.2
  • Google Play Services 25
  • Google Repository 19

2015/08/26 "Support library 23 and SDK 22/23": Currently the latest support library version available is 23. This version requires you to build with SDK 23 but Fennec does not build with that SDK version just yet. You can find more about that in this mailing list posting. If you are seeing the following build error then you will need to manually downgrade your support library to version 22:

   /usr/local/opt/android-sdk/extras/android/support/v7/appcompat/res/values-v23/styles_base.xml:20: error:
   Error retrieving parent for item: No resource found that matches the given name 'android:Widget.Material.Button.Colored'.
   /usr/local/opt/android-sdk/extras/android/support/v7/appcompat/res/values-v23/styles_base_text.xml:19: error:
   Error retrieving parent for item: No resource found that matches the given name 'android:TextAppearance.Material.Widget.Button.Inverse'.

"Google Play Services" is listed under Extras by the android package manager.

You should ensure that the Support Library and SDK versions match. If you update the Support Library but don't switch to a later SDK, you'll get errors that mention a newer version than your SDK, like this:

  .AccessibilityNodeInfoCompatApi22: can't find referenced method
  'void setTraversalAfter(android.view.View,int)' in class 

In the event that the NDK and SDK versions listed here are out of date, you can always find the canonical version numbers that Mozilla uses to build Fennec in automation. Look for the following variables:


bug 1108782 tracks listing and enforcing these version requirements in the source code.

Advanced topics


You can optionally install ccache, which can make rebuilding Firefox faster after you have built it once and don't change (much) of the C++ source code. In general, ccache is not a performance improvement if you use only one object directory, or edit only Java and/or JavaScript source code.

If you want to use ccache, add a line the following to your mozconfig:

ac_add_options --with-ccache[=/optional/path/to/ccache]

The default cache size of 1GB is not large enough for a Fennec build. To fully utilize ccache (generally meaning you can expect full builds to complete in <5 minutes from a populated cache), you'll need to change the cache size to at least 4GB. Do so by running:

ccache --max-size 4G

On Mac OS X, install ccache like:

brew install ccache

On Debian-like Linuxes, install ccache using:

sudo apt-get install mercurial ccache

Enabling C++ debugging

If you want to create a build suitable for debugging the C++ code, add:

ac_add_options --enable-debug-symbols

Building for the x86 architecture

If you want to build for x86, substitute:

ac_add_options --target=i386-linux-android

for the target specified above. Note: you cannot use ac_add_options --disable-optimize when building for x86. See bug 965870.

Building for the ARMv6 architecture

ARMv6 is no longer a supported target as of Firefox 33.

If you want to build for ARMv6 instead of ARMv7 (only required for very old, very low end phones), add:

ac_add_options --with-arch=armv6

Unsupported build flags

Do not specify these flags because the resulting build will cause out-of-memory crashes:

ac_add_options --disable-install-strip # Do not use!

Updating the builders` SDK

i.e. Nightly builds & treeherder. See Mobile/Fennec/Android/Updating_SDK_on_builders.


Don't set CC / CXX environmental variables

If you've set the environmental variables CC and CXX (e.g. via .bash_aliases or via your mozconfig), then you probably need to unset them before building for Android, or else your build may fail with something like:

checking whether the C compiler (gcc -mandroid -fno-short-enums (etc etc)) works... no

followed by errors about "C compiler cannot create executables", "Relocations in generic ELF (EM: 40)", and "crtbegin_dynamic.o: error adding symbols: File in wrong format". This is a sign that you're compiling with your platform's native compiler (due to having CC / CXX set), instead of the android-specific GCC version that ships with the NDK. See bug 977817 for more details; as noted there, the build system may trust your custom CC & CXX variables, when you probably don't want it to.

Common how-tos

Add an Android string resource

  1. Add an XML string entity to mobile/android/base/locales/en-US/android_strings.dtd with the English string you want to add.
  2. Add a <string> element to mobile/android/base/
  3. Build using mach build mobile/android/base or your IDE.

Your new string should appear in org.mozilla.gecko.R.string. Here's an example patch that adds the single string pref_private_data_syncedTabs.

Why is this necessary? Mozilla's main localization process is based on XML entities. Localization teams localize the XML entity definitions using existing tools, but they do not see strings.xml itself. Building prepares the final strings.xml for use. You can be sure your changes are in place by finding your entity and string in $OBJDIR/mobile/android/base/res/values/strings.xml.

Modify an existing Android string resource

  1. Find the relevant <string> element in mobile/android/base/
  2. Find the underlying English string entity in mobile/android/base/locales/en-US/android_strings.dtd. Usually, you'll see <string>&string_entity&semi;<string>; the string entity is string_entity.
  3. If your change is just fixing a typo (spelling error, capitalization, whitespace), just update the android_strings.dtd.
  4. If you are really changing the string, you also need to change the entity name. It's traditional to add or increment a trailing integer, like string_entity2.
  5. Build using mach build mobile/android/base or your IDE.

Your updated string should appear. Here's an example patch that changes several strings, including renaming tab_queue_notification_text_singular to tab_queue_notification_text_singular2.

Why is this necessary? Mozilla's localization process only recognizes new string entities, not modified string entities. (The old, unused entity is automatically ignored and eventually deleted.)

Add a new Robocop test

  1. Add a Java test file named like mobile/android/tests/browser/robocop/ This will get your test compiled into the Robocop APK.
  2. Add your test file/name section like [testMyThing] to mobile/android/tests/browser/robocop/robocop.ini. Without this, the Robocop test harness will not know about your test!
  3. Optionally add HTML, JS, and CSS resources to folder mobile/android/tests/browser/robocop.
  4. Run mach build to get them built/installed before running your test.
  5. Run mach build build/mobile/robocop to update the Robocop APK.
  6. Make sure you have host binaries downloaded and configured, following Host Builds (MOZ_HOST_BIN).
  7. Run mach robocop testMyThing to run your new test on your device.
  8. Iterate!

Here's an example patch that adds a fairly complicated new testSelectionCarets test.

See also some tips on writing UITests.

Copy a profile from your phone

E.g., to explore with sqlite3. Use Copy Profile.


Developing Fennec with IDEs

Fennec has support for developing using IntelliJ (Ultimate and Community Edition) and Android Studio. (We also have some legacy support for Eclipse, but you should prefer using IntelliJ or Android Studio.) Get started Developing Fennec with IDEs.

Finding relevant code

Almost all of the Fennec-specific code is in the mozilla-central source tree under:


Of particular interest to most new contributors will be:

mobile/android/base/ # the main Android activity that starts when you open Fennec
mobile/android/chrome/content/browser.js # the main JavaScript file that controls Gecko to make it do what we want

If you are looking for something specific, use the code-search tool at to search for relevant pieces of code.


For the JavaScript parts of the code base, remote debugging with a desktop version of Firefox is the most effective way to see what is going on, add breakpoints, etc.

For Android Java code, if you have IntelliJ set up, the debugger works well and allows you to set breakpoints, inspect variables and objects, etc. Debugging without an IDE is much more primitive, and you can try using Android Log statements and inspecting logcat.

Coding Style


Follow the Mozilla Coding Style.

XML files (layout, resources, styles, etc)

  • Each child tag should be indented with 4 spaces.
  • The properties should be aligned with the first property of a tag.
  • Each element should have "android:id" first, "style" (if exists) second, and the other properties follow. The root will have "xmlns:android" as first property.
  • A Line break after every tag.

Common nits

Check for these nits before asking for review for a patch:

  • Remove trailing whitespace
  • Spacing
    • Four spaces for Java indent (for main Fennec code - android-sync github project has different spacing)
    • Around operators (+, -, etc.) and :
    • Between comment "//" and text
  • Braces for Java if statements, even if they are one line
  • Comments should be full sentences (capitalization, punctuation)
    • Good comments are useful and clear even for someone reading a particular area of code for the first time
  • Avoid using single-letter variables in almost all cases - it makes code harder to read

Closing resources

When handling resources (like Cursors), a try/finally block should be used to ensure these are closed properly. For example:

final Cursor c = getCursor();
try {
} catch (SomeSpecificException sse) {
} finally {

Once the try block is entered, the finally block will *always* get executed upon exit of the try block. The one exception is if there is a System.exit call inside the try block, which immediately exits the program and makes everything moot anyway. The finally block will get executed on caught and uncaught exceptions, as well as normal returns.

If you are casting the resource to something, make sure that you do the cast inside the try block, like so:

// GOOD!
InputStream is = getInputStream();
try {
    FileInputStream fis = (FileInputStream) is;
} finally {

rather than doing this:

// BAD!
FileInputStream fis = (FileInputStream) getInputStream();
try {
} finally {

This is so that in case of ClassCastExceptions you don't get a dangling open resource left behind.

Caveats for Timing

TLDR: Google recommends using SystemClock.uptimeMillis() for general purpose interval timing of user interface events or performance measurements. If you're adding stuff for timing, use SystemClock.uptimeMillis(), rather than something like new Date().getTime().

Normally in Java the default time-getter is System.currentTimeMillis() since it avoids the overhead of creating a new Date object. This is also what new Date() does under the hood. However, currentTimeMillis() and the Date object are both subject to change in unexpected ways if the user changes the time on their device, or if daylight savings comes into effect, or there's a network time update, or whatever. So Android has generously provided android.os.SystemClock which has various functions that you can use to get a better timestamp. Refer to the class javadoc and pick whichever function is most suitable for what you're trying to measure.

Multilocale builds

  • Create a directory, clone mozharness, copy the config file for easy editing/usage:
mkdir multilocale
cd multilocale
hg clone
cp mozharness/configs/multi_locale/
  • Edit
    • currently will check out m-c into a directory named 'mozilla-central' in this directory
    • currently assumes your mozconfig is in this directory and named 'mozconfig'
    • currently assumes your mozconfig sets your objdir name to 'objdir-droid'
  • pull mozilla-central
mozharness/scripts/ --cfg --pull-build-source
# Alternately, you can hg clone
  • Run the script, which will create a multilocale apk
mozharness/scripts/ --cfg

And you're done.

  • If you want to recompile or re-run the script, restore your objdir to en-US first!
mozharness/scripts/ --cfg --restore-objdir

Also see this blog post for more information.

Single-locale language repacks

There is a script in mozharness for this (scripts/ but it relies on buildbot information so it's not suitable for local repacks.

This assumes that $(AB_CD) is the locale you want to repack with; I tested with "ar" and "en-GB".

  • clone l10n-central/$(AB_CD) so that it is a sibling of your mozilla-central directory
  • I assume your object directory is "objdir-droid" and that you have built and packaged already
make -f && make -C objdir-droid package
  • copy your .mozconfig to .mozconfig.l10n and add the following lines
# L10n
ac_add_options --with-l10n-base=../../l10n-central

# Global options
ac_add_options --disable-tests

mk_add_options MOZ_OBJDIR=./objdir-l10n
  • cd to mozilla-central
  • configure and prepare objdir-l10n
MOZCONFIG=.mozconfig.l10n make -f configure
make -C objdir-l10n/config
  • copy your built package into objdir-l10n
cp ./objdir-droid/dist/fennec-*en-US*.apk ./objdir-l10n/dist
  • unpack. This files objdir-l10n/dist with the bits of the APK, ready for re-assembling.
make -C objdir-l10n/mobile/android/locales unpack
  • compare locales (you may need to install the compare-locales tool first). This writes locale differences into objdir-l10n/merged.
compare-locales -m objdir-l10n/merged mobile/android/locales/l10n.ini ../l10n-central $(AB_CD)
  • finally, re-assemble with the locale differences
LOCALE_MERGEDIR=objdir-l10n/merged make -C objdir-l10n/mobile/android/locales installers-$(AB_CD)

You should find an APK at "objdir-l10n/dist/fennec-*$(AB_CD)*.apk".


See Mobile/Fennec/Android/Testing.


Using logcat

logcat is a tool that is going to show you some logs prompted by the device. It might be a good help if you don't want to or can't run gdb. You can use it by running this command:

 adb logcat -v time

You can make things appear in logcat using printf_stderr. With debug builds, NS_WARNING, NS_ERROR and NS_ASSERTIONS will show up in logcat. If you're trying to debug something, you may wish to pipe the logcat output through grep to filter out irrelevant things (most Fennec-related output will be viewable by

 adb logcat -v time | grep Gecko

but remember that when attaching log output to a bug you should include unfiltered output as there may be relevant log entries under other tags.

Using other logcat apps

ICS (4.1) and below
  • Install the aLogCat app. Use it to capture logs and attach the logs to bugs.

Once you have alogcat installed, just use Fennec as you would normally. Upon encountering a bug or issue, start the aLogcat app (as soon as possible after seeing the Fennec issue) and select "Share" or "Save" from the menu to send it via email or save it to the SD card. The log can then be attached to a bug or sent to a developer. As with adb logcat, it is better to have a log with timestamps than without timestamps. To enable timestamps in the log, select "Preferences" from the aLogcat menu, and change the "Format?" option to "Time".

If you need to, you can search for some kinds of Fennec-related output by using the "Filter" menu item and entering "Gecko". However, when submitting logs for bug reports, please make sure you clear the filter and include all of the available log data.

Jelly Bean (4.2) and above

JavaScript dump()

To use the dump() function in JavaScript to write to the log:

  1. Go to about:config and set browser.dom.window.dump.enabled to "true"
  2. Run the following ADB commands:
adb shell stop
adb shell setprop log.redirect-stdio true
adb shell start

Using JimDB

See Mobile/Fennec/Android/GDB

Using Debug Intent

Note: this is not useful with JimDB. If you want to use JimDB, just start it.

In order to attach before things get running, launch with:

  adb shell am start -a org.mozilla.gecko.DEBUG -n org.mozilla.fennec_foobar/.App

(Replace foobar by your username)

and just click launch once gdb is attached. If you need to debug a crash that happens before XRE_Main is called, the patch on bug 572247 may be useful.

this script [1] will attach gdbserver for you

Getting dalvik java stack dumps using gdb

(gdb) call dvmDumpAllThreads(true)

this will dump a stack trace to logcat

Note: this will only work if you have symbols for dalvik.

Debugging with jdb

JimDB can now launch JDB integration

You can also use eclipse for debugging in a similar way by setting up for debugging "Remote Java application".

Debugging with eclipse

You need to find the PID of your fennec process. Forward it to a local TCP socket as in "Debugging with jdb."

In Eclipse switch to the debug perspective. Go to Run > Debug configurations... Remote Java Application. Change the port to the TCP port you specified in your adb command. Under Source, navigate to your checkout, then into mobile/android.

Eclipse looks for source code in a specific location. You need to create the directory hierarchy:

       gecko -> ../../base

That is, in mozilla-central/mobile/android, create org/mozilla, and put the symlink gecko pointing to mozilla-central/mobile/android/base.

You may also want to add more debugging information and can do that like this:

diff --git a/config/ b/config/
index 4591239..a47726a 100644
--- a/config/
+++ b/config/
@@ -70,6 +70,6 @@ JAVAC_FLAGS = \
   -classpath $(JAVA_CLASSPATH) \
   -bootclasspath $(JAVA_BOOTCLASSPATH) \
   -encoding UTF8 \
-  -g:source,lines \
+  -g:source,lines,vars \
   -Werror \

Arguments and Environment Variables

If you need to set an environment variable at run time, append --es env# VAR=VAL to your activity manager command where # is the ordered number of variables for example:

 adb shell am start -a android.activity.MAIN -n org.mozilla.fennec_$USER/.App --es env0 VAR=val --es env1 FOO=bar

If you need to pass arguments at run time, append --es args "<your-args>" to your activity manager command. For example, to launch with a specific profile:

 adb shell am start -a android.activity.MAIN -n org.mozilla.fennec_$USER/.App --es args "--profile /mnt/sdcard/myprofile"

To launch with a specific URL, use the am -d option to set the intent's data URI:

 adb shell am start -a android.activity.MAIN -n org.mozilla.fennec_$USER/.App -d ''

PR Logging

You can use the env vars as described above to enable NSPR logging:

 adb shell am start -a android.activity.MAIN -n org.mozilla.fennec_$USER/.App --es env0 NSPR_LOG_MODULES=all:5 --es env1 NSPR_LOG_FILE=/mnt/sdcard/log.txt

If no file is specified, logging is directed to the android logs:

 adb shell am start -a android.activity.MAIN -n org.mozilla.fennec_$USER/.App --es env0 NSPR_LOG_MODULES=all:5

Look for lines marked "PRLog" in the adb logcat output.

Using legacy GDB (non-JimDB)

See Fennec/Android/GDBNoRoot

Reading back the framebuffer

If you need to verify what is in the back buffer at a particular time, you can cleverly call functions from gdb to allocate memory, read back, and write that to disk.

You need to know the size of your framebuffer a priori; in this case, it's 480x699.

You also need to know what the GL enum values are, because unless you compile with -ggdb, you don't have #defines available to you in the debugger. Very helpful information: GL_RGBA = 0x1908, GL_UNSIGNED_BYTE = 0x1401. The rest you can find in gfx/gl/GLDefs.h.

You should be able to call glReadPixels directly, but in my experience that causes Fennec to crash. However, if you have a GLContext* lying around, as you often do, you can work around that problem.

(gdb) set $m = (int*)malloc(480*699*4)
(gdb) call aManager->mGLContext.mRawPtr->fReadPixels(0, 0, 480, 699, 0x1908, 0x1401, (void*)$m)
(gdb) set $f = fopen("/sdcard/outputfile", "wb+")
(gdb) call fwrite($m, 1, 480*699*4, $f)
$7 = 1342080
(gdb) call fclose($f)
$8 = 0

Now there is a file called /sdcard/outputfile that you can adb pull. But since it's just raw RGBA values, you need to be able to wrap that in PNG headers to display it. Jeff Muizelaar wrote a header called minpng.h that you can use to do so.

Get Jeff's minpng.h, and put it in a directory along with a driver c program:

#include "minpng.h"

int main(int argc, char* argv[])
	FILE* f = fopen(argv[1], "rb");
	int w = atoi(argv[2]);
	int h = atoi(argv[3]);
	char* d = (char*) malloc(w * h * 4);
	fread(d, w * h * 4, 1, f);
	write_png(argv[4], d, w, h);

Compile and run:

$ gcc -o minpng minpng.c
$ ./minpng outputfile 480 699 output.png

Using Rendertrace (Maple)

Rendertrace is a utility that will dump layer position and timing information (such as drawing, upload) to the console. This information can pasted into the rendertrace web front end to visualize the layer position and event timeline. This will let you understand where you're gecko is spending its time and why were checkerboarding.

To enable go in 'gfx/layers/RenderTrace.h' and uncomment '#define MOZ_RENDERTRACE'. Rebuild and run 'adb logcat | grep RENDERTRACE', paste the result in and hit 'reload'. For details talk to BenWa.

Using apitrace

Apitrace is a tool for tracing GL/EGL calls for debugging purposes. It basically uses an interim shared library called libapitrace that contains shadow gl* and egl* functions, which then get logged and then passed through to the real driver.

Use apitrace from to build for desktop and android.

apt-get install libegl1-mesa-dev libgles1-mesa-dev libgles2-mesa-dev libqt4-dev cmake
git clone
cd apitrace

# Build for Android
cmake -DANDROID_NDK=/path/to/your/ndk -DCMAKE_TOOLCHAIN_FILE=android/android.toolchain.cmake -DANDROID_API_LEVEL=9 -Bbuild-android -H.
make -C build-android -j8

# Build for desktop
cmake -H. -Bbuild
make -C build -j8

export EGL_SOFTWARE=true
./build/eglretrace -v /path/to/your/apitrace_log.trace

The Android build will create in build-android/wrappers, which you can then push to your device to /data/local:

adb push build-android/wrappers/ /data/local/tmp

Restarting Fennec will cause it to load the apitrace library and the apitrace log will be saved to /data/data/org.mozilla.fennec_username/firefox.trace

You can then adb pull /data/data/org.mozilla.fennec_username/firefox.trace and analyse it on your desktop.

You can also use qapitrace as a GUI to inspect your trace files. (be sure to switch qapitrace to the EGL api using the options dialog)

These instructions provide a trace that does not include the Java GL code. To get traces including java code is more complicated. You need to use the patch from this bug and this version of Further, you'll need to build your own image/modify the current one to replace /init.rc. You also need to disable hardware acceleration of the UI ( Ask jrmuizel for more information if you want to do this.


about:memory provides heaps (ha!) of useful memory information.

You can obtain a snapshot of memory info from a running Fennec instance using:

 adb shell am broadcast -a org.mozilla.gecko.MEMORY_DUMP

This dumps a json file to the SD card and prints out the exact filename to logcat. You can pull the json file to desktop using

 adb pull <absolute-path-to-file>

and view it in firefox's about:memory: use the "Read reports from a file" option at the bottom of the about:memory page.



Debugging Java code with DDMS


Other useful tips and tricks


There are some addons which may be useful for development purposes. See Mobile/Fennec/Android/Development/Addons.

Tweaking UI prefs

By default, all of these prefs are set to "-1" in Fennec, meaning they take the values listed below, which are maintained in

Fractional values are specified in 1/1000th of a value; to specify a value of 0.3, write 300.

Note: You need to restart Fennec after changing these values.

Pref Default value Description
ui.scrolling.friction_slow 850 This fraction in 1000ths of velocity remains after every animation frame when the velocity is low.
ui.scrolling.friction_fast 970 This fraction in 1000ths of velocity remains after every animation frame when the velocity is high.
ui.scrolling.velocity_threshold 10 Below this velocity (in pixels per frame), the friction changes from friction_fast to friction_slow.
ui.scrolling.max_event_acceleration 12 The maximum velocity change factor between events, per ms, in 1000ths.
ui.scrolling.overscroll_decel_rate 40 The rate of deceleration when the surface has overscrolled, in 1000ths.
ui.scrolling.overscroll_snap_limit 300 The fraction of the surface which can be overscrolled before it must snap back, in 1000ths.
ui.scrolling.min_scrollable_distance 500 The minimum amount of space that must be present for an axis to be considered scrollable, in 1/1000ths of pixels.
gfx.displayport.strategy 1 The strategy we use to determine how display ports are calculated. 0 = fixed margin, 1 = velocity bias, 2 = dynamic resolution, 3 = no margins
gfx.displayport.strategy_fm.multiplier 1500 When gfx.displayport.strategy = 0 (fixed margin), the 1000th of each dimension of the viewport the displayport is sized to.
gfx.displayport.strategy_fm.danger_x 100 When gfx.displayport.strategy = 0 (fixed margin), the 1000th of the width of the viewport the horizontal danger zone is set to.

Danger zone is defined as the space at the edge of the viewport at which the viewport (and hence displayport) starts being changed.

gfx.displayport.strategy_fm.danger_y 200 When gfx.displayport.strategy = 0 (fixed margin), the 1000th of the height of the viewport the vertical danger zone is set to.
gfx.displayport.strategy_vb.multiplier 1500 When gfx.displayport.strategy = 1 (velocity bias), the 1000th of each dimension of the viewport the displayport is sized to.
gfx.displayport.strategy_vb.threshold 32 When gfx.displayport.strategy = 1 (velocity bias), the threshold for velocity, in pixels/frame, when multiplied by the screen DPI.
gfx.displayport.strategy_vb.reverse_buffer 200 When gfx.displayport.strategy = 1 (velocity bias), the fraction of the buffer (in 1000ths) to be kept in the direction opposite the direction of the scroll.

Invalidate the JavaScript startup cache

To make life easier for developers, in local development builds only, bug 976216 invalidates the JavaScript startup cache every time Firefox for Android starts. On non-local development builds (including TBPL builds and try builds), the JavaScript startup cache is not invalidated at startup.

Background: JavaScript files and modules (like browser.js) are cached for fast startup. The cache is invalidated only when an internal build ID is updated, which only happens when certain C++ code is rebuilt. That doesn't happen for most patches that only touch Java and JavaScript within mobile/android. See bug 695145 for the details of this build ID handling. If you happen to be building a non-local development build in some way, you might need to invalidate the JavaScript startup cache by touching toolkit/xre/nsAndroidStartup.cpp and rebuilding libxul.

killer script

if [ $# -ne 1 ]
    echo "usage: $0  packagename.of.your.activity"
    echo "for example:"
    echo "  $0 org.mozilla.fennec"

p=`adb shell ps | grep $1 | awk '{print $2}'`
if [ "$p" = "" ];
    echo "ERROR: That doesn't seem to be a running process. Please make sure your"
    echo "application has been started and that you are using the correct"
    echo "namespace argument."

adb shell run-as $1 kill $p


This is an example .gdbinit that uses the symbols from a locally built rom and automatically attaches to gdbserver. Note that putting a .gdbinit file inside a directory will make gdb load it thus you will not pollute your regular gdb init with those configurations.

set solib-search-path /home/blassey/android/system/out/target/product/passion/symbols/system/bin:/home/blassey/android/system/out/target/product/passion/symbols/system/lib/:/home/blassey/src/ndk5-m-c/objdir-droid-dbg/dist/bin
set solib-absolute-prefix /home/blassey/android/system/out/target/product/passion/symbols/system/lib/
target remote localhost:12345

Rooting Android devices

See Rooting Android Devices.

Sign a Fennec build

Nightly builds are available unsigned, so that you can sign them with your local debug key and install them on top of your own debug builds (without uninstalling and losing your profile). To sign and install the unsigned nightly build:

 jarsigner -sigalg SHA1withRSA -digestalg SHA1 -keystore ~/.android/debug.keystore -storepass android -keypass android gecko-unsigned-unaligned.apk androiddebugkey
 zipalign -f -v 4 gecko-unsigned-unaligned.apk gecko-signed-aligned.apk
 adb install -r gecko-signed-aligned.apk

Or you can also re-sign a signed build. If "fennec.apk" is signed already, this will remove the signature and replace it with your own. The result will be saved as "fennec-resigned.apk":

 zip fennec.apk -d META-INF/*
 jarsigner -sigalg SHA1withRSA -digestalg SHA1 -keystore ~/.android/debug.keystore -storepass android -keypass android fennec.apk androiddebugkey
 zipalign -f -v 4 fennec.apk fennec-resigned.apk

If you get this error when you try to sign a package:

 jarsigner: unable to sign jar: invalid entry compressed size (expected 16716 but got 16964 bytes)

You should to follow some steps to complete your task:

* rename the .apk to .zip
* unzip the file in some folder
* remove the METAINF folder
* zip the remaining files
* change the name .zip to .apk
* sign again

To verify if everything is alright use the command

 jarsigner -verbose -verify