it's saved me many times too
I've linked to several great blog posts on Firefox 3 features lately, but there's one piece of an older feature that doesn't get enough credit. I got a reminder this morning when Firefox crashed (a flash bug that may have just been fixed,) while I was composing a rather long webmail message and just this evening read this blog post.
If you haven't needed to experience Firefox's crash recovery because you're never crashing, great. If you have, though, it sure is nice that it saves your work.