Why does Firefox crash on my Macbook?

For some reason after about half an hour of using Firefox, it will stop fully loading pages. I have to keep hitting refresh multiple times to finally get a page to display everything in the correct format, and then when I click on another link, Firefox wont fully load that page.

I tried reinstalling it, and upgrading to Firefox 3 (which is amazing), but that didn’t seem to work. The only temporary solution I can find is restarting my computer. Should I completely delete it from my computer and then reinstall?