Firefox 3.6 is built on Mozilla's Gecko 1.9.2 web rendering platform, which has been under development since early 2009 and contains many improvements for web developers, add-on developers, and users. This version is also faster and more responsive than previous versions and has been optimized to run on small device operating systems such as Maemo.

Notable Firefox 3.6 features include:

* Available in more than 70 languages - get your local version.
* Support for a new type of theme called Personas, which allow users to change Firefox's appearance with a single click.
* Protection from out-of-date plugins to keep users safer as they browse.
* Open, native video can now be displayed full screen and supports poster frames.
* Improved JavaScript performance, overall browser responsiveness, and startup time.
* The ability for web developers to indicate that scripts should run asynchronously to speed up page load times.
* Continued support for downloadable web fonts using the new WOFF font format.
* Support for new CSS attributes such as gradients, background sizing, and pointer events.
* Support for new DOM and HTML5 specifications including the Drag & Drop API and the File API, which allow for more interactive web pages.
* Changes to how third-party software can integrate with Firefox in order to prevent crashes.