Thunderbird Gets Inline Spell Checker
Okay, it's not in the nightlies yet, but Scott MacGregor has released a Windows build of Thunderbird with the new inline spell-checker he's been working on for the last few weeks. Since it's built into the core editing component rather than tacked on as an extension this should ultimately be less buggy than previous attempts (read: not buggy at all).
It's still in the early testing phase; it's not even checked into the nightlies yet, but it's a good indication of what's to come. If this gets ported to Firefox for its text fields I'll be very happy indeed. Actually that's not unlikely as Asa was lamenting the lack of features in Firefox's editing controls.