I had the same problem, then I loaded FasterFox, an add-on that you can get from Mozilla site.
Give it aa try before you dump Firefox, it made an incredible difference for me!
https://addons.mozilla.org/en-US/firefox/addon/9148
FasterFox extension is no longer supported. It NEEDs to be removed.
However, FastestFox is a new extension that takes over where FasterFox ended. Install that, enjoy.