If Firefox is starting to feel a little slow, FireTune might be able to help. It helped me. FireTune is a free utility you can use to speed up Firefox. It works on both the 1.x and 2.x version of Firefox. It doesn't change the binaries at all, so all of the changes are easy to remove if needed which makes this a low risk proposition. When I used FireTune on my system, Firefox was noticeably faster afterwards.