>>I didn't use too many - about half of them work, some got replacements, others later.
>
>All extensions I'm using got upgrade to work with FF3.

The ones that still don't are the ones I can live without (like Firebug - I'll need something like that next time I develop a web app, not sooner), with the honorable exception of mouse gestures, which I really wish I had again. There seem to be nice replacements available.

Other than that, everything important does work.