I thought I would post this announcement in the off topic section since a lot of WP.com members use Firefox...
From the Official Mozilla blog
Firefox 4 Beta 1 is now available and ready for testing. This first version is filled with dozens of new features and improvements.
Quote Source → http://blog.mozilla.com/blog/2010/07/08/more-details-on-features-in-firefox-4-beta-1/
Firefox 4.0b1 download site link → http://www.mozilla.com/en-US/firefox/beta//
Firefox 4.0b1 release notes link → http://www.mozilla.com/en-US/firefox/4.0b1/releasenotes/
Since most Firefox extensions won't work with the latest beta version you will need to download the "Add-on Compatibility Reporter 0.5" to be able to use Extensions that other wise would not work with the latest beta version...
You find the extension here → https://addons.mozilla.org/en-US/firefox/addon/15003/?src=external-fxbetarelnote