Firefox 9 was released on December 20, 2011; version 9.0.1 was released a day later and is currently the latest stable version in the "Release" channel.The latest version of Firefox has the following changes:
* Added Type Inference, significantly improving JavaScript performance
* Improved theme integration for Mac OS X Lion
* Added two finger swipe navigation for Mac OS X Lion
* Added support for querying Do Not Track status via JavaScript
* Added support for font-stretch
* Improved support for text-overflow
* Improved standards support for HTML5, MathML, and CSS
* Fixed several stability issues
* Fixed several security issues
source:http://linuxpoison.blogspot.com/2011/12/13578167756065.html