Hi,
you can manually delete all the Firefox files you don't need (make sure you don't delete them all by leaving at least Firefox 3.0 !) and as for the thing about constantly entering passwords etc, you need to go to > edit > preferences > and check exactly what settings you have because I have mine set to delete all online info including passwords after leaving Firefox.
So check out your Privacy and Security settings I think that's where you will find the problem.
Hope this helps and have a good one.
