SpeedyFox is an excellent free app that allows you to defragment Firefox user profiles containing your bookmarks, history, cookies, passwords... in order to speed up the opening and execution of the browser.
Start by downloading the app SpeedyFox :
Then run it.
Select the profile to defragment and then simply click on Speed Up My Firefox! and wait a few seconds.
You must close Firefox before defragmentation.
Then click on Run Firefox and that’s it!
For testing this application under MacOS X Snow Leopard, the result is blatant: more than 10 seconds before to launch Firefox, almost instantaneous now!
An operation repeated from time to time to keep Firefox always at the top of its shape!