Firefox

A few weeks ago I switched my web browser to Firefox. I do like it, although it's taken some getting used to. I was doing just fine with it until today when, suddenly, my scroll wheel on my mouse won't work when using Firefox. It will work in any other program I have tried it in, but not in Firefox. Any ideas out there as to why this is happening? I just downloaded the newest version of FF thinking that this might help, but it didn't. Any info would be greatly appreciated!! Thanks!