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.

Key resources

Firefox developer guide

Our developer guide explains how to get Firefox source code, how to build it on Linux, macOS and Windows, how to find your way around, and how to contribute to the project.

Firefox add-on guide

The Add-on guide provides information about developing and deploying Firefox extensions.

Developer release notes

Developer-focused release notes; learn what new capabilities for both websites and add-ons arrive in each version of Firefox.

Firefox channels

Firefox is available in five channels.

Firefox Nightly

Each night we build Firefox from the latest code in mozilla-central. These builds are for Firefox developers or those who want to try out the very latest cutting edge features while they're still under active development.

Download Firefox Nightly

Firefox Developer Edition

This is a version of Firefox tailored for developers. Firefox Developer Edition has all the latest developer tools that have reached beta. We also add some extra features for developers that are only available in this channel. It uses its own path and profile, so that you can run it alongside Release or Beta Firefox.

Download Firefox Developer Edition

Firefox Beta

Every four weeks, we take the features that are stable enough, and create a new version of Firefox Beta. Firefox Beta builds are for Firefox enthusiasts to test what's destined to become the next released Firefox version.

Download Firefox Beta


After stabilizing for another four weeks in Beta, we're ready to ship the new features to hundreds of millions of users in a new release version of Firefox.

Download Firefox

Firefox Extended Support Release (ESR)

Firefox ESR is the long-term support edition of Firefox for desktop for use by organizations including schools, universities, businesses and others who need extended support for mass deployments.

Download Firefox ESR


Experimental features in Firefox

This page lists Firefox's experimental and partially implemented features, including those for proposed or cutting-edge web platform standards, along with information on the builds in which they are present, whether or not they are activated "by default", and which preference can be used to activate or deactivate them. This allows you to test the features before they are released.

Firefox release notes for developers

Below you'll find links to the developer release notes for every Firefox release. These lovingly-crafted notes provide details on what features and APIs were added and improved and what bugs were eliminated in each version of Firefox. All written to give developers like you the information they need most. You're welcome.

See also