This is about to drive me crazy. I have Fedora 9 and Firefox 3.0.1. Everytime I scroll up using the middle mouse button it takes me to the previous web page. It's like I hit the back button. I've gone to about:config and tried changing each middlemouse option. That didn't work. I've got to Preferences and enabled autoscrolling. That didn't resolve it. I've tried changing the general.autoScroll option. No luck there.

Can anyone tell me where in Firefox I can go to change the middle mouse button's behavior so that when I scroll up, it actually scrolls the page up?

http://kb.mozillazine.org/Mouse_Tips

I take it your trouble is with a scrollwheel, not a center-button?
This LQ thread discusses the same problem (scroll wheel acts as back-button), with solutions.

In firefox type in the address 'about:config'

Double-click the line
mousewheel.horizscroll.withnokey.action. Set it to 0
(2 is forward and back pages. 1 enables Horizontal scrolling).

Set mousewheel.horizscroll.withnokey.sysnumlines to true

Thanks for the advice. I had a chance tonight to boot that workstation up and strangely enough the problem had disappeared. Perhaps I had failed to restart the x server one last time or maybe it was the KVM. Don't know.