It's most likely your computer. With my old computer I had to tweak Firefox to get it to run faster. With my new computer I haven't even bothered with the tweaks as I doubt there is anything that would make this beast faster. But even with the old machine, while the tweaks were cool and worth while, it wasn't all that necessary.
Try the tweaks first:
http://www.metacafe.com/watch/322730/how_to_make_mozilla_firefox_run_much_faster/
Watch the video with a pad of paper to write down the instructions. It might not be a bad idea to watch it a few times first before applying the tweaks. Also, I remember that some of it wasn't exactly what I saw in the settings (probably due to the video being for an older version of FireFox) but it was all there, I just had to reason out a few things. If this causes you trouble I can go through it again and make notes of what I figured out.
If this doesn't help, then I would recommend that you first clear out your cache, then before running the browser again you defrag your computer.
If these don't help, we'll go from there.
Tommy
Probably.
Give firefox a chance. I really like it the best of all of them (including Safari), and I think most people would agree.
Tommy