They're coming thick and fast! It's a bug-fix release with an improved default theme and fixes to the extension manager.
I found 0.9 much buggier than 0.8, so I hope this release is better.
[edited by: bull at 3:05 pm (utc) on June 29, 2004]
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7) Gecko/20040626 Firefox/0.9.1
My 0.9 didn't register as 0.8 - are you sure you weren't using a release candidate?