Some handy FF extensions I found;

Tab Preferences
Tab Browser Extensions
Windows Update (near the bottom of the Page)
Addblock
Download Manager Tweak
Fire FTP
Spellchecker (thanks to Morbo)
Tweak Network settings

Just a few here but have a look and you find quite a lot of them that maybe handy to you <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />
Oh and btw most of these have nightlies (updates nearly every night)

Mea Culpa's Demesne Note; artwork for Avatar courtesy of NWN and CEP Old Elven Saying: "Never say Never if you're gonna live forever!!!" "I didn't do it, it wasn't my fault"