how to page back in browser

How can I assign a button on my mouse to page back in my web browser? It was automatically configured in windows and I never really realized how dependent upon it I really am. I'm using firefox right now until I can figure out safari.

Thanks

USBOverdrive should do the trick.

Thanks,

I installed it today, works great! It's just what I needed.

MagicMouse does it with 2 finger swipe which is neat.