At long last, K‘s tabbed-browsing plugin MiniT has been updated (to v 0.4) so that it plays well with FireFox 1.0 (and the latest 1.0.1). In the meantime, I had been using the feature rich but slightly less graceful Tab Mix. Guess what? You can use them both simultaneously, if you like (not sure if this is idea, but it hasn’t hurt anything yet).
Another essential goodie: SpellBound, though a little trickier to install than your average plugin, lets you check the spelling of any form textbox! It does a very solid and unobtrusive job (just adds a “check spelling” item to your context menu).