I've discovered an add-on that outdoes SpeedyFox by a lightyear; it's called Speedfox and it works automatically....once installed, it doesn't require any special attention.
It's available at Mozilla's FF add on page.
Been using it for the past week w/ FF 9(Aurora) and have been experiencing absolutely no slowdowns whatsoever. Definitely worth checking out!

Amazing! First launch of Firefox was faster than Safari's.

Seems to work if you use speedyfox each time you open firefox. If you keep speedyfox in your applications folder then you use up as much time finding it, starting it, push the speed up firefox button the push the run firefox button.
Takes as long as just starting firefox to begin with.

Seems to reduce or eliminate the frequency of the SPOD I normally get with lots of tabs open in FF.

YMMV.

This seems to be an sqlite vacuum thing:
http://blog.opencomponentry.com/2009/11/09/script-to-vacuum-os-x-sqlite-databases/

That will take care of all the sqlite databases (will speed up Mail and iPhoto as well as Firefox)