Firefox can now migrate your bookmarks, history, and cookies from Google Chrome
NEW
With Sync enabled, add-ons can now be synchronized across your computers
NEW
The CSS text-size-adjust property is now supported
HTML5
The outerHTML property is now supported on HTML elements
HTML5
View source syntax highlighting now uses the HTML5 parser (see bug 482921)
DEVELOPER
The Style Editor for CSS editing is now available to web developers
DEVELOPER
Web developers can now visualize a web page in 3D using the Page Inspector 3D View
DEVELOPER
SPDY protocol support for faster page loads is now testable
DEVELOPER
XMLHttpRequest now supports HTML parsing
DEVELOPER
Files can now be stored in IndexedDB (see bug 661877)
DEVELOPER
Websockets has now been unprefixed
FIXED
Redesigned media controls for HTML5 video
FIXED
Firefox notifications may not work properly with Growl 1.3 or later (691662)
 

Hier ist die komplette Changelog der Beta aufgelistet (ziemlich umfangreich):
http://www.mozilla.org/en-US/firefox/11.0beta/releasenotes/