Firefox Workflow

This article outlines the recommended workflow for interacting with the Firefox repository (mozilla-unified.

Optimally Configure Mercurial

When you run or mach bootstrap (if you already have a clone), the bootstrapper will prompt you to run a Mercurial configuration wizard. You should run this wizard and make sure it is happy about your Mercurial state.

You should also run mach bootstrap periodically to ensure Mercurial support files are up-to-date.


The instructions in this article assume the firefoxtree extension is installed. Please activate it when the wizard prompts you to!

Cloning the Repository

Clone the Firefox repository by running:

$ hg clone firefox
$ cd firefox

Feature Development

So you want to start work on a new Firefox feature? This section is for you.

Start by obtaining the latest code so you aren’t working on old and possibly stale code:

$ hg pull

Then update to the tip of mozilla-central:

$ hg up central

Now, change some stuff. We assume you know how to do this.

Commit your changes:

$ hg commit
<type commit message in editor>

Make more changes and keep committing:

$ hg commit
<another commit message>

Push your changes to MozReview to initiate code review:

$ hg push review


We assume you’ve followed the MozReview User Guide to configure MozReview.

OK. Progress on that feature is blocked waiting on review. It could take a while for that to happen. Let’s start working on something else. We always start by pulling the latest code so our change isn’t out of date before we’ve event started.:

$ hg pull
$ hg up central
<change stuff>
$ hg commit
<change stuff>
$ hg commit
$ hg push review

Changing Code After Reviews

A review comes back. Unfortunately review was not granted and you need to make changes. No worries.

We need to update the working directory to the changeset to be modified so we can edit them. How you do this depends on how you are tracking commits. For most workflows, we recommend hg wip (see Workflows for more on this command) to find them. e.g.:

$ hg wip
o   6139:5060abe260e9 gps  vcsreplicator: explicitly record obsolescence markers in pushkey messages
: o   5940:e16f6960cdeb gps  hgmo: update automationrelevance for Mercurial 3.8; r?smacleod
: o   5939:e62f4eb60ef3 gps  mozhg: fix test output for Mercurial 3.8; r?glob
: o   5938:f71be022e59c gps  global: upgrade Mercurial to 3.8.3 (bug 1277714)
o   5937:5a8623230b7a gps  pushlog: convert user and nodes to bytes (bug 1295724); r=smacleod
: o   5717:9c2ca05479e9 gps  hgmo: handle obsolete changesets (bug 1286426); r?glandium

If you want to edit e16f6960cdeb, you would hg up e16f6960cdeb.

Or if you are using bookmarks, you can update directly to the bookmark:

$ hg up my-bookmark
4 files updated, 0 files merged, 0 files removed, 0 files unresolved
(activating bookmark my-bookmark)

Now that your working directory is updated, you can start making changes.

You have several options available to you. If you know the changes are small and won’t conflict if reordered, go ahead and make them now and commit:

<make changes>
$ hg commit
<make more changes>
$ hg commit

Then squash the changesets together:

$ hg histedit


For hg histedit to work without arguments, you’ll need Mercurial 3.7 or newer.

You’ll then need to:

  1. Reorder your fixup changesets to occur immediately after (below) the changesets they will be modifying.
  2. Set the action on these fixup changesets to roll so they are fully absorbed into the changeset that came before.

Alterantively, you can edit changes directly. Again, use hg histedit. But this time, change the action of the changesets you want to modify to edit. Mercurial will print some things and will leave you with a shell. The working directory will have been updated to the state of the commit you are editing. If you run hg status or hg diff you will see that this changesets’s changes are applied to files already. Make your changes to the files then run hg histedit --continue to continue with the history editing.


Advanced users can use the evolve extension <> to edit changesets in place. Because this is still an experimental feature, it isn’t documented here.

Once all the changes are made, you’ll want to submit for review again:

$ hg push review

Then we’re back to waiting.


You finally get review and can land your changes!

The easiest way to do this is through the use of Autoland. You can access Autoland through the Land Commits option of the Automation menu. Clicking this button displays a dialog containing a list of commits to be landed. MozReview will attempt to automatically rewrite the commit messages to reflect who reviewed which commit. If everything looks good, click the OK button and the autolander will land your commits for you.

Autoland will attempt to rebase you commits on the head of the autoland repo for you automatically. If it can’t do this (say there was a file merge conflict during the base), an error will (eventually) be displayed in MozReview and you will have to rebase yourself and push the result back to MozReview and try the autoland request again.


Only landing to the autoland repo is supported. This is because we will be removing integration repos in the future so the history of mozilla-central isn’t linear and free of merge commits.

If Autoland succeeds, Pulsebot will comment in your bug that your changes have landed. Unfortunately, there is not currently any notification that Autoland has failed outside of MozReview, so if the trees are open and your changes have not landed within a few minutes, please check back in MozReview to see if any errors have occurred.

Manual Reviewer Attribution and Landing

Unable to use Autoland? Follow these instructions.

Update to the tip-most changeset that will land (often a head) after finding the changesets using the technique in the previous section:

$ hg up <SHA-1 or label>

Before landing, we need to rebase our unlanded changesets on top of the latest changeset from an integration branch:

$ hg pull
$ hg rebase -d inbound

If you need to add r= reviewer attribution to the commit message, do that now:

$ hg histedit

Change the action to m for all the changesets and proceed to update commit messages accordingly.

And finally we land:

$ hg push -r . inbound