Firefox was always like that for me, even on a Mac. So I switched to Camino, but that's not an option for you. You might like Opera—it's super fast.

Have you tried removing all your various 3rd party plugins? Alternately, perhaps uninstall FF and reinstall after a restart. I can imagine a scenario where an in-use .DLL doesn't get upgraded properly by the automatic updater or some such shenanigans.

If you do go back, try the IE 7 beta. The tabbed browsing in IE 7 is superior to FF, in my opinion, although I've got something funky going on with my History in 7B, so it's not all gravy yet.

I'm going to second Opera. Give it a try. It's so fast and easily customizable and doesn't use the same amount of resources Firefox does. I tend to go back and forth between both, since I like Sage much more than Opera's built in RSS aggregator but Opera is my overall favorite.

I've always had problems with Firefox. It is slow and bloated.

Opera crashes from time to time, but it's not nearly as bloated and laggy as Firefox, so I will third that suggestion.

And I will fourth it. Opera is the good. Like candy is good. But keep a copy of FF around for folks that don't like to code to web standards. But on most sites, it works great.

(XP, 2 GHz pentium, 256 MB ram.)
There's your problem, right there (the 256 MB RAM part). XP is very unhappy with anything less than 512 MB and Firefox adds to the problem hugely. My experience is that you cannot run Firefox effectively on a machine that is short on RAM. With more RAM, I would almost guarantee that the problems will go away.

Delete your firefox user profile folder. That usually does the trick.

Try K-Meleon It's a lightweight Mozilla-based browser for Windows. Configurable to the point of complete dorkiness.

seanyboy: Wouldn't deleting the profile folder also delete all of my bookmarks?

Yes it would. If you can find a way of exporting and then re-importing, do this.
I assumed, as you were moving to a different browser that you wouldn't mind losing them.

Cleaning a Firefox profile.

This is basically the #1 thing to do when Firefox gets all sluggish. You can test it by running firefox.exe -profilemanager and creating the fresh one first, and if you notice it whizzing like a Formula 1 racer, it's your profile.

I've been having alot of issues with FF lately, the non-quitting thing is really annoying and I've had to force quit it several times after it stopped actually doing anything.

I've had better success if I empty to cache but it is still getting to the point where I'm starting to check out the other hot browsers out there and see if they want to tango.

Camino is the way to go on Mac. FF on Mac has been terrible but it's improved in the last release, for some reason. I have only a few problems with FF on my Windows machine with 1G of RAM but it's still slow to start up. More RAM makes everything suck less.

I've good things about K-Meleon, too. Also, Opera has been getting a lot of praise for its speed and RAM footprint so it's worth checking out if the profile trick doesn't work for you.

You can always export your bookmarks to the desktop (or other folder) before deleting the profile and import them into the new browser, so that should not be an issue.

I went to that profile cleaning page, and it doesn't look like anything that exists on my machine. I tried just copying my bookmarks.htm file and then deleting the profile, but nothing seems to have changed. Maybe I'll try the more-RAM thing.

To save your bookmarks go here and save them, then import them into your new profile.