Contributing to open source in Firefox(Mozilla): how do I find the relevant portion of the Mozilla code base where a bug occurs in order to fix

Question

I am trying to contribute to open source particularly Firefox(Mozilla), I have done my installation and set up but I have a challenge determining where to look in the codebase to find the file where a bugs occurs in order to propose a patch. I would greatly appreciate general guidance on how to proceed. This is my first time attempting to contribute to open source with Firefox.

Basically, upon seeing the bug as reported in Bugzilla(a website where mozilla bugs are reported), I am clueless on how to proceed from there.

Answer 1

welcome to SO!

I know that contributing to such a big codebase can sometimes feel overwhelming, but I can guarantee you that the Firefox devs really appreciate the efforts you are already putting (and will put!) in your contribution. So.. thanks for the help!

General tips

1. Firefox codebase is huge, complex and has many moving parts. Downloading and getting Firefox correctly built locally is already a big step forward, and will save you time later. If you haven't done that already, consider doing it!

2. Read the How To Contribute Code To Firefox documentation page. It gives a good overview of how a code contribution process looks like in Firefox.

3. Don't feel shy about asking questions! The bug on Bugzilla (or the github ticket) is usually a good place to ask specific questions or general directions on how to fix a bug in Firefox, and folks are generally friendly, inclusive and happy to support you support them!

   a. If you don't receive a direct response within a few business days (usually 2-3) from somebody on the bug, chances are the notification got swallowed in the "immense sea of notifications, emails, messages"(tm) that devs receive. See the next section about reaching out.

How to find who to talk to?

Who knows about a specific part of Firefox or any Mozilla product? This could seem like an hard thing to figure out, but there's a few tips.

• If the bug report is on Bugzilla, good people to talk to would be the Reporter (if they are a Mozilla contributor) or the Triage Owner.

• Mentored bugs are bugs that were triaged by the dev teams and that were designated to introduce folks to the codebase. For this bugs, a "Mentor" is usually shown under "Assignee" in the "People" section of the bug. That's a good person to ask questions!
• Mozilla publishes the list of folks who are responsible about components in Firefox. You can find who to talk to based on where the code is/the bug was filed and then consulting this page.
• You can send direct request over Bugzilla to individuals, they are called "needinfo requests". After logging into Bugzilla, on the specific page of the bug you need information on, scroll to the bottom. Type your question in the "Add comment" section, tick the "Request information from" checkbox and either pick the role of the person you want to flag from the dropdown, or select "other" and paste an email address there (that you have identified using the previous points). If the person is on bugzilla, the text field will autocomplete and show the relevant person.

• If all the above fails, you can rely synchronous communication and chat with the devs over here in the # developers channel.

How to find what code to change?

1. If it's not in the bug, ask the reporter or the person responsible of that section of code. For bugs marked as "mentored", ask the assigned Mentor!
2. If the bugzilla bug doesn't mention specific files and you want to find out yourself without reaching out, your best ally is Searchfox. You can type some keywords from the bug at the top of the page and wait for the results in the codebase to come in. This is highly effective! If the bug asks changing CSS files, for example, you could add a file filter like *.css in the top right.
3. Another pro-tip is looking at what other bugs in that same bugzilla product/component touched. You would find that by clicking on the arrow next to the component, then picking "Recently Fixed Bugs in This Component": it will show a list of fixed bugs, you can pick one or more, then look at the attachments.

Hope this helps!