Firefox is Mozilla's popular Web browser, available for multiple platforms including Windows, macOS, and Linux on the desktop and all Android and iOS mobile devices. With broad compatibility, the latest in Web technologies, and powerful development tools, Firefox is a great choice for both Web developers and end users.

Firefox is an open source project; much of the code is contributed by our huge community of volunteers. Here you can learn about how to contribute to the Firefox project and you will also find links to information about the construction of Firefox add-ons, using the developer tools in Firefox, and other topics.

Learn how to create add-ons for Firefox, how to develop and build Firefox itself, and how the internals of Firefox and its subprojects work.

  • Project documentation

    Get detailed information about the internals of Firefox and its build system, so you can find your way around in the code.

  • Developer guide

    Our developer guide provides details on how to get and compile the Firefox source code, how to find your way around, and how to contribute to the project.


Experimental features in Firefox
This page lists features that are in Nightly versions of Firefox along with information on how to activate them, if necessary.
Firefox and the "about" protocol
There is a lot of useful information about Firefox hidden away behind the about: URL protocol. The most useful is the URL about:config, which displays preferences and settings that can be inspected and changed.
Firefox UI considerations for web developers
There are a number of places within the Firefox user interface where web sites are listed for the user to choose a destination to visit or a site to manage in some way. One example is the new tab page, which includes a "Top Sites" section showing sites you visit that Firefox thinks you're likely to want to visit again, as well as potentially some sites that have been pinned to always appear in that space.
Linux compatibility matrix
The following table lists the available library versions for the Firefox builds dependencies, and/or to build Firefox.
Multiple Firefox profiles
A profile in Firefox is the collection of settings, customizations, add-ons, and other personalizations that a user has made or installed into their copy of Firefox. You can find details about profiles on Mozilla's end-user support site.
Performance best practices for Firefox front-end engineers
This guide will help Firefox developers working on front-end code produce code which is as performant as possible—not just on its own, but in terms of its impact on other parts of Firefox. Always keep in mind the side effects your changes may have, from blocking other tasks, to interfering with other user interface elements.
This document lists privacy-related documentation.
Security best practices for Firefox front-end engineers
This article will help Firefox developers understand the security controls in place and avoid common pitfalls when developing front-end code for Firefox.
Site Identity Button
The Site Identity Button is a feature in Firefox that gives users more information about the sites they visit.

Firefox profiles

If you find yourself using multiple Firefox channels—or just multiple configurations—on a regular basis, you should read how to use multiple Firefox profiles by turning Firefox's Profile Manager and other profile management tools to your advantage.

See also