Firefox has two main release channels:

• Firefox: Simply named Firefox, this is the default channel and is the one recommended. It’s the stable branch with the latest features available. Once a new release is out, the older release immediately stops receiving support and everyone must migrate to the next Firefox release.

• Firefox Extended Support Release (ESR): is an official version of Firefox developed for large organizations like universities and businesses that need to set up and maintain Firefox on a large scale. Firefox ESR does not come with the latest features, but it has the latest security and stability fixes. Usually these branches are supported for a year, with a planned release calendar for new ESR branches. For more information you should review the release cycle documentation.

Firefox also has three testing channels:

• Firefox Beta: This branch is meant to reflect what the next Firefox release will look like. Every four weeks it gets cherry-picked changes from Nightly, then follows a three weekly point release aimed at stabilizing the release for the stable branch. Version number is always X + 1, X being the Firefox version number.

• Firefox Developer Edition: This branch is based off the Firefox Beta branch with additional DevTools merged in. It gets released alongside the Firefox Beta release, following the same release pattern. Version number is always X + 1, X being the Firefox version number.

• Firefox Nightly: This is the branch that receives all the changes before anything else. It gets daily updates which represent the master branch. This is the branch that first features new changes/features, which then may be forwarded to Firefox Beta after being tested. Version number is always X + 2, X being the Firefox version number.

Special notes

• Firefox 78 ESR is the last version of Firefox that supports Flash. The last version of that ESR will be 78.15, which is scheduled to be released on 2021-10-05. This means that Flash will officially be out of support on Firefox when Firefox 78 ESR reaches EOL on 2021-11-02.
• Firefox 78 ESR is the last version of Firefox that supports macOS versions < 10.12.
• Firefox only supports last 3 macOS releases, matching the Apple support cycle.
• On iOS Firefox is forced by Apple to use WebKit rendering engine instead of Firefox’s own Gecko, for similar reasons browser-addons are not allowed on iOS unlike on Android. Both of these limitations are due to Apple’s rules for submitting apps to the App Store.