Aha! Firebug slows down JavaScript even if it’s not active on the current page. That explains a LOT! # Facebook & Gmail run so slowly in Firefox on my home computer that I’ve been running them exclusively in Opera (and now Chrome). This is almost certainly the cause.
Update: Apparently that’s not it, since I had both the console and script panels disabled as described in that article. Oh, well.
that’s too bad. The only other thing I can recommend is trying the newer 3.6 betas if you haven’t already. We’ve made some big performance improvements there.