https://developer.mozilla.org/devnews/index.php/2009/03/12/firefox-31-beta-3-now-available-for-download/

* Improved the new Private Browsing Mode, including the ability to “Forget This Site” from the History sidebar.
* Improved performance and stability with the new TraceMonkey JavaScript engine.
* Improvements to web worker thread support.
* New native JSON support.
* Improvements to the Gecko layout engine, including speculative parsing for faster content rendering.
* Support for new web technologies such as the video and audio elements, the W3C Geolocation API,
JavaScript query selectors, CSS 2.1 and 3 properties, SVG transforms and offline applications.

Good news is a good portion of my addons kept working which is sweet...

Delicious
Grease Monkey
sxipper
web developer toolbar
clipmarks