According to Mozilla, the latest version of FireFox will come with several new enhancements and performance tweaks. This includes improved JavaScript execution speed of around 20%-30%, additional support for HTML5 and CSS, improved theme integration along with support (finally) for Mac OS X Lion, which means that OS X Lion users will be able to perform two finger swipe navigation between pages.
Full release notes for FireFox 9 can be found on Mozilla’s website along with the download (Windows / Mac / Linux).