This beta is now available in 54 languages - get your local version.
Added functions to make it easy to clear recent history by time as well as remove all traces of a website.
New support for web worker threads.
Improvements to the Gecko layout engine, including speculative parsing for faster content rendering.
Removed the new tab-switching behaviour based on feedback from users
The Firefox 3.1 Beta 2 is a free download for all platforms; if you decide to test it, be sure to back up your Mozilla profile (or maybe wait for the portable version release).
Firefox 3.1 Beta 2 English/US download