Have you tried running Firefox without all the addons /themes enabled to see if this speeds up usage.

To do this go to Start / Run / Programs / Mozilla Firefox / Mozilla Firefox (Safe Mode).

If this speeds things up disable all of your addons etc. in the full version. Then re-enable them one at time to see which one is causing the problem.

Having a ship load of tab's open slows you down as well in Firefox...

yea I tried disabling the addons about an hour ago but it didn't work. sometimes it runs really slow and sometimes it runs normal. when it is slow it sometimes takes up to 5 minutes to load a page.

That sound more like a connection to your ISP problem, than a Firefox problem...

The other computers on my network are running Firefox just fine. I tried to reset my router but it didn't work.

The only other thing I can suggest you try, is uninstall firefox including addons (save the bookmarks html file first).

Then re-install Firefox on another partition or drive, I have used this method before as it writes up different registry info.

This has solved several problems that people have encountered...

"Then re-install Firefox on another partition or drive" how do you do that?