Mozilla Central Quick Start

Table of contents

Firefox Developer Git Quick Start Guide

Getting setup to as a first time Mozilla contributor is hard. There are plenty of guides out there to help you get started as a contributor, but many of the new contributor guides out of date often more current ones are aimed at more experienced contributors. If you want to review these guides, you can find several linked to from Working on Firefox.

This guide will take you through setting up as a contributor to mozilla-central, the Firefox main repository, as a git user.


The first thing you will need is to install Mercurial as this is the VCS that mozilla-central uses.


brew install mercurial
sudo port install mercurial


sudo apt-get install mercurial

Alternatively you can install Mercurial directly.

Check that you have successfully installed Mercurial by running:

hg --version

If you are an experienced git user and are unfamiliar with Mercurial, you may want to install git-cinnabar. Cinnabar is a git remote helper that allows you to interact with Mercurial repos using git semantics.


There is a Homebrew install option for git-cinnabar, but this did not work for me, nor did the installer option. Using these tools, when I tried to clone the Mercurial repo it hung and did not complete. I had to do a manual install before I could use git-cinnabar successfully to download a Mercurial repo. If you would like to try either of these option, however, here they are:


brew install git-cinnabar

All Platforms

git cinnabar download
Manual installation
git clone && cd git-cinnabar
export PATH="$PATH:/somewhere/git-cinnabar"
echo 'export PATH="$PATH:/somewhere/git-cinnabar"' >> ~/.bash_profile
git cinnabar download

git-cinnabar’s creator, glandium, has written a number of posts about setting up for Firefox Development with git. This post is the one that has formed the basis for this walkthrough.

In synopsis:

  • initialize an empty git repository

git init gecko && cd gecko
  • Configure git:

git config fetch.prune true
git config push.default upstream
  • Add remotes for your repositories. There are several to choose from, central, inbound, beta, release etc. but in reality, if you plan on using Phabricator, which is Firefox’s preferred patch submission system, you only need to set up central. It might be advisable to have access to inbound however, if you want to work on a version of Firefox that is queued for release. This guide will be focused on Phabricator.

git remote add central hg:: -t branches/default/tip
git remote add inbound hg:: -t branches/default/tip
git remote set-url --push central hg::ssh://
git remote set-url --push inbound hg::ssh://
  • Expose the branch tip to get quick access with some easy names.

git config remote.central.fetch +refs/heads/branches/default/tip:refs/remotes/central/default
git config remote.inbound.fetch +refs/heads/branches/default/tip:refs/remotes/inbound/default
  • Setup a remote for the try server. The try server is an easy way to test a patch without actually checking the patch into the core repository. Your code will go through the same tests as a mozilla-central push, and you’ll be able to download builds if you wish.

git remote add try hg::
git config remote.try.skipDefaultUpdate true
git remote set-url --push try hg::ssh://
git config remote.try.push +HEAD:refs/heads/branches/default/tip
  • Now update all the remotes. This performs a git fetch on all the remotes. Mozilla Central is a large repository. Be prepared for this to take a very long time.

git remote update

All that’s left to do now is pick a bug to fix and submit a patch.