Mozilla released Firefox 9 on Tuesday, the latest version of its popular web browser. Firefox 9 adds several enhancements, but perhaps the most notable is its improved JavaScript engine that reportedly offers up to a 30% performance boost (in Kraken and V8 benchmarks) on Javascript-heavy sites. The browser also adds OS X Lion optimizations that should improve two-finger swipe navigation and theme support. Other features include support for font-stretch, improved support for text-overflow, improved support for HTML5, MathML and CSS, and stability fixes. Firefox 9 is available for free now and builds are available for Mac, Linux and Windows.