There are loads of ways to speed up Firefox. The easiest way would simply be to download
Fasterfox and set it to turbocharged. That's what I do, saves you remembering what you changed and works just as well.
Also stume, when you visit a large amount of sites often, it will help quite a bit. You notice the speed up when you're visiting lots of pages very quickly (forums, galleries). Pipelining and connection width are two of the simplest, but Fasterfox automates it all.