Order maybe of most common usage :-
FDM - use all time for RS links
Download Helper - great for YouTube, GoogleVid etc - no hassle at all just works
Flashblock - superb - just puts an F in place of flash, if you want it hit the F, otherwise just ignore
FEBE - invaluable and easy to use - every time I add an extension or change bookmarks I update
QuickJava - only run with JS when necessary, and almost NEVER with Java
AdBlockPlus - probably use this more than I think I do
Greasemonkey - great for those little extra scripts you need from time to time
YesPopups - another of those probably used a lot more often than I realize !!
Anyone know a way of getting a different search engine on two different FF windows or tabs ??
Great forums !!