I've just discovered Firefox 3.1 BETA 2 portable
) is out, so I just had to go and test (Follow the instructions here
to run the beta concurrently to your 3.0 installation).
As most people are likely aware, Firefox 3.1 will include a new private browsing mode
(known to many as "porno mode") which will see your browser forget everything that you did while it was enabled. This feature is now available in BETA 2. From the tools menu, select "Private Browsing". Firefox will revert back to your current session when you're finished.
Many will be thanking the gods that 3.1 now includes preliminary support for Web Workers
They've removed the new tab switching behavior shown here in post 1
due to negative user feedback.
The support for HTML 5 elements is now completely stable (as far as my experience goes). Give them a try yourself here