And it turns out that beyond simply clearing the cache or something like that, you need to find the download.sqlite file and delete it yourself. Doing so returned basic functionality to my browser, but between this and its unwillingness to load gmail at times (for some reason igoogle then clicking on the gmail link works) Firefox has been very frustrating lately.
Apparently, it’s a common enough problem that access to the solution will be even easier to get in 3.6.
If you’re a fairly vanilla Firefox user, I have to put in a plug for Opera. Great browser, built-in mouse-gestures, imo one of the better password managers, built-in magnifying, and also the joy that is Speed Dial. If you haven’t tried Opera in a while, give Opera 10 a shot.
However, if you use a lot of Firefox extensions (there’s an extension for everything, including Speed Dial) Opera is pretty lacking. Low user base = far fewer developers.