Firefox 3.6 is the last major version of an official Firefox release to run on PowerPC-based Macintoshes (see TenFourFox for a much-more-recent version of Firefox for PowerPC-based computers running Mac OS X). It was superseded by Firefox 4, released the next year, although Fx 3.6 had a prolonged period of use and version 4 had noted user interface changes.

This was to allow users to receive new features more quickly and the dawn of a new roadmap that reflected these changes. As well as receiving major updates, the browser also received minor updates with new features. This release marked the beginning of a new development cycle for Firefox.

In this version, support for X BitMap images was dropped. It uses the Gecko 1.9.2 engine (compared to 1.9.1 in Fx 3.5), which improves compliance with web standards. The release's main improvement over Firefox 3.5 is improved performance (due to further speed improvements in the TraceMonkey JavaScript engine). Mozilla Firefox 3.6 is a version of the Firefox web browser released in January 2010.

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