Building Firefox in 2024
I wanted to build Firefox from source this week, and thought I’d write about it since there were a few things that were non-obvious to me.
Getting the source
Follow Mozilla’s documentation for your platform on this. You’ll need mercurial and python3 at least.
Just make sure when you bootstrap the code, you bootstrap it to use git - their documentation describes how, it’s something like:
$ python3 bootstrap.py --vcs=git
Firefox is migrating to git, so it’s likely that these instructions will be out of date by the time you read this. More on that here:
Building Firefox
There are some tips on building firefox in slightly different ways, such as downloading pre-built artifacts, etc. I did try those at first, but then I found that hardware acceleration didn’t work, so I ended up removing all those options and building normally instead.
Firefox has a pretty easy build system, just run ./mach build and off it goes.
Configure your build with mozconfig
You’re building firefox from source, so I presume you want to customise it. Well, you do that with a file called mozconfig. Just whack that in your mozilla-unified repository, and any options set in there will be read when you ./mach build.
You can list most of the options with:
$ ./mach configure -- --help
Some options I recommend for building a release copy of firefox:
# Enable Profile Guided Optimisation. Basically, after building firefox, it runs
# firefox with a suite of tests, profiles it, and then re-compiles with that
# added information.
# https://firefox-source-docs.mozilla.org/build/buildsystem/pgo.html
ac_add_options MOZ_PGO=1
# Always bootstrap toolchain, so we don't depend on the host's toolchain.
# This makes the build download the toolchain and uses that instead, which makes
# things a whole lot simpler.
ac_add_options --enable-bootstrap
If you want to do a debug build instead of a release build, then add ac_add_options --enable-debug.
How to build a different version of Firefox
If you’ve just checked everything out, then you should be on the bookmarks/central branch. If you build now, you’ll get the latest Firefox Nightly. But, what if you want to build the latest release? What about the Beta? Or the latest Extended Support Release?
This was non-obvious to me at the beginning, but if you are using git just list the remote branches:
# list remote branches
$ git branch -r
origin/HEAD -> origin/branches/default/tip
origin/bookmarks/aurora
origin/bookmarks/autoland
origin/bookmarks/beta
origin/bookmarks/central
origin/bookmarks/fx-team
origin/bookmarks/inbound
origin/bookmarks/release
origin/bookmarks/esr115
...
And checkout the particular branch you want to build.
Keep in mind that branches have different build configurations. For example, the bookmarks/release branch doesn’t automatically include --enable-bootstrap like the bookmarks/central branch does.
I recommend just keeping --enable-bootstrap in there since it means you don’t need to make any changes to your machine’s build system.
Where to ask for help
The firefox maintainers are extremely helpful, and should you have any questions at all I wouldn’t hesitate to ask. If it’s related to building firefox itself, I found asking questions in the #developers channel worked very well.
Huge thanks for everyone working on firefox - it’s a great piece of technology, and surprisingly easy to get setup and build things locally for a project of its age.
Last updated: Tuesday, February 13, 2024 at 20:41