According to the developers, the list of improvements for Firefox 3.1 Beta 1 includes the following:
– Web standards improvements in the Gecko layout engine
– Added support for CSS 2.1 and CSS 3 properties
– A new tab-switching shortcut that shows previews of the tab you’re switching to
– Improved control over the Smart Location Bar using special characters to restrict your search
– Support for new web technologies such as the <video> and <audio> elements, the W3C
These being the fact, all hopes are now moved to late November, when the second beta is scheduled to arrive.
Firefox 3.1 Beta 1 is available here for download.