This page should guide you through the initial steps of contributing to Mozilla. Welcome, we're delighted to see you! :)

Need help?

The Mozilla community prides itself on being an open, accessible, and friendly community for new participants. If you have any difficulties getting involved or finding answers to your questions, please bring those questions to the #introduction chat room on, where we can help you get started.

We know even before you start contributing that getting set up, to work on Firefox and finding a bug that's a good fit for your skills, can be a challenge. We're always looking for ways to improve this process: making Mozilla more open, accessible and easier to participate with. If you're having any trouble following this documentation, or hit a barrier you can't get around, please contact Mike Hoye at We're determined to solve hurdles for new contributors.

What skills do I need?

Mozilla is a large project and we are thrilled to have contributors with very diverse skills:

  • If you know C++, for instance, you can contribute to the core layers of Firefox and other Mozilla products
  • If you know JavaScript, or HTML/CSS, you can contribute to the front-end of Firefox
  • If you know Java, you can contribute to Firefox Mobile, Firefox on Android, and MozStumbler
  • If you know Swift, you can contribute to Firefox for iOS and Firefox Focus for iOS
  • If you know Python, you can contribute to our web services, including Firefox Sync, or Firefox Accounts
  • If you know Make, shell, Perl, or Python, you can contribute to our build systems, release engineering, and automation
  • If you know C, you can contribute to NSS, Opus, and Daala
  • If you know Rust, you can contribute to rustc, Servo: the web browser engine designed for parallelism and safety, or Quantum: the project to bring large pieces of Servo to Gecko
  • There are even many ways to contribute to the Mozilla mission without programming. If getting involved in design, support, translation, testing, or other types of contributions sparks your interest please see the Volunteer Opportunities page

Perhaps you do not know programming yet, but you want to start learning? There are plenty of resources available on the Mozilla Developer Network!

Step 1 - Build Firefox for Desktop or Android.

If you'd like to contribute to Firefox, simple instructions to build desktop Firefox are here, and mobile contributors can get started here to build Firefox for Android. Getting set up may take some time, there are some big downloads involved, so you may want to move on to the next steps while it builds. Additional build instructions can be found here.

Mozilla's other products, including the community-supported Thunderbird builds, can be found with a quick search. Often you won't need to build anything to start making a contribution.

Step 2 - Find 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.

Fix your pet peeve

If there's something 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:

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:

  • 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
  • Mentored bugs - are more challenging, but have a mentor who commits to helping you through the process. Generally, there should be enough information in the bug to get started. Whenever you need help, contact the mentor over IRC, in the bug itself, or by email. When you've completed the bug, they will help you get your code into the tree
  • Follow @StartMozilla on Twitter - we link up Good First Bugs for new contributors across Mozilla every day
  • Visit - 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, and one for implementing new applications

Use a bug searching tool

There are several tools developed by members of the Mozilla community. These help
new contributors find bugs to work on, without having to use Bugzilla's more perplexing search component.

Step 3 - Fix the bug

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

Step 4 - Get your code reviewed

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

We now favor using our code review platform MozReview.
You can still submit a manual patch, but MozReview is absolutely preferred.
Check the MozReview documentation on Creating commits and Submitting review requests.

You can attach a patch to the bug and ask for a review. Do this by clicking the Details link on your attachment, then set the review flag to ?, and enter the reviewer's bugzilla ID in the text field that appears (either their email address or the :UniqueName they provide). It is very important to attach a bugzilla ID, or the request will be missed.

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 and look for the people who have touched the functions you're working on. They too are good candidates
  • 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

Step 4b - Follow it up

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 then you can ask for help on IRC in the #introduction, or #developers channels, or contact Mike Hoye directly.

Step 5 - Respond to the review

For most new contributors, even for long time Mozillians, the first review of your patch will be an "r-". 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! Attach the new patch to the bug again, and ask for a further review from the same reviewer. If they give you an r+, this means your bug is accepted into the tree!

Step 6 - Getting code into the tree

Once your patch has received an r+, 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 adding the checkin-needed keyword, to the "keywords" field at the top of the bug. 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.

Step 7 - Repeat

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 push your own code, after it has been read.

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: