How To Contribute Code To Firefox

The whole process can be a bit long, and it might take time to get things right. If at any point you are stuck, please don’t hesitate to ask at https://chat.mozilla.org in the #introduction channel.

We make changes to Firefox by writing patches, testing them and pushing them into “the tree”, the term we use for all the code in Mozilla-Central. Let’s get started.

Please see the Firefox Contributors Quick Reference for simple check list.

Finding something to work on

Bugs listed as ‘Assigned’ are not usually a good place to start, unless you’re sure you have something worthy to contribute. Someone else is already working on it!
Even with no assignee, it is polite to check if someone has recently commented that they’re looking at fixing the issue.
Once you have found something to work on, go ahead and comment! Let the bug submitter, reviewer, and component owner know that you’d like to work on the bug. You might receive some extra information, perhaps also made the assignee.

Find a bug we’ve identified as a good fit for new contributors.

With more than a million bugs filed in Bugzilla, it can be hard to know where to start, so we’ve created these bug categories to make getting involved a little easier:

  • Codetribute - our site for finding bugs that are mentored, some are good first bugs, some are slightly harder. Your mentor will help guide you with the bug fix and through the submission and landing process.

  • Good First Bugs - are the best way to take your first steps into the Mozilla ecosystem. They’re all about small changes, sometimes as little as a few lines, but they’re a great way to learn about setting up your development environment, navigating Bugzilla, and making contributions to the Mozilla codebase.

  • Visit firefox-dev.tools - we list Firefox Developer Tools bugs for new contributors.

  • Student Projects - are larger projects, such as might be suitable for a university student for credit. Of course, if you are not a student, feel free to fix one of these bugs. We maintain two lists: one for projects based on the existing codebase.

Fix that one bug

If there’s one particular bug you’d like to fix about Firefox, Thunderbird, or your other favorite Mozilla application, this can be a great place to start. There are a number of ways to do this:

Fixing your bug

We leave this in your hands. Here are some further resources to help:

Getting your code reviewed

Once you fix the bug, you can advance to having your code reviewed.

Mozilla uses Phabricator for code review.

Who is the right person to ask for a review?

  • If you have a mentored bug: ask your mentor. They will help, or can easily find out. It might be them!

  • Run hg blame on the file and look for the people who have touched the functions you’re working on. They too are good candidates. Running hg log and looking for regular reviewers might be a solution too.

  • The bug itself may contain a clear indication of the best person to ask for a review

  • Are there related bugs on similar topics? The reviewer in those bugs might be another good choice

  • We have an out of date list of modules, which lists peers and owners for the module. Some of these will be good reviewers. In a worst case scenario, set the module owner as the reviewer, asking them in the comments to pick someone more suitable

Please select only one reviewer.

Following up and responding

Once you’ve asked for a review, a reviewer will often respond within a day or two, reviewing the patch, or saying when they will be able to review it, perhaps due to a backlog. If you don’t hear back within this time, naturally reach out to them: add a comment to the bug saying ‘review ping?’, check the “Need more information from” box, and add the reviewer’s name. If they don’t respond within a day or two, you can ask for help on Matrix in the #introduction:mozilla.org or #developers:mozilla.org channels, or contact Mike Hoye directly.

Don’t hesitate to contact your mentor as well if this isn’t moving.

For most new contributors, and even for long-time Mozillians, the first review of your patch will be “Requested Changes” (or an “r-” in Bugzilla). This does not mean you’ve done bad work. There is more work to do before the code can be merged into the tree. Your patch may need some changes - perhaps minor, perhaps major - and your reviewer will give you some guidance on what needs to be done next.

This is an important process, so don’t be discouraged! With our long-lived codebase, and hundreds of millions of users, the care and attention helping contributors bring good patches is the cornerstone of the Mozilla project. Make any changes your reviewer seeks; if you’re unsure how, be sure to ask! Push your new patch up to Phabricator again and ask for a further review from the same reviewer. If they accept your changes, this means your patch can be landed into the tree!

Getting code into Firefox

Once your patch has been accepted, it is ready to go. Before it can be merged into the tree, your patch will need to complete a successful run through our try server, making sure there are no unexpected regressions. If you don’t have try server access already, your mentor, or the person who reviewed your patch, will be able to help.

Once you have a green try server run, mark that your patch is ready to commit by

  1. opening the Phabricator page for your patch

  2. clicking the ‘Edit Revision’ link in the sidebar on the right

  3. then into the ‘Tags’ field and

  4. typing ‘Check-In Needed’ to get the tag added.

A friendly Mozillian, with commit access, will be along shortly to push your patch to the repository, and update the bug as required. If your patch passes all Mozilla’s automated testing, it will soon be merged into the main branch, and become a part of the Nightly build.

Do it all again!

Thank you. You’ve fixed your very first bug, and the Open Web is stronger for it. But don’t stop now.

Go back to step 3, as there is plenty more to do. Your mentor might suggest a new bug for you to work on, or find one that interests you. Now that you’ve got your first bug fixed you should request level 1 access to the repository to push to the try server and get automated feedback about your changes on multiple platforms. After fixing a nontrivial number of bugs you should request level 3 access so you can land your own code after it has been reviewed.

More information

We’re in the process of improving information on this page for newcomers to the project. We’ll be integrating some information from these pages soon, but until then you may find them interesting in their current form: