Overall stability is good and I have not noticed any leakage yet. Menu opening and closing seems snappier too. You can read all about new features and download it from here:
There’s a bunch of significant improvements to CSS support.
I have not yet tried the privacy browsing mode…that sounds interesting although not very useful for me. For public computers in wifi shops I suppose that might be cool.
Most add-ons for FF3 do not enable immediately in 3.1, although Firebug does so that’s really all I need.
The only negative I see is that once again there is virtually no documentation on how to upgrade a linux client to the beta. Yeah yeah…I know I can do it, but why should linux people have to find their way in the dark without a decent installer or at least a set of bullets. Sheesh…