Firefox is wayyyy too big.

I recently installed Firefox into my new computer, which runs Windows Vista. When I open Firefox, all web pages are displayed nearly twice as big as they should be and the toolbars at top take up nearly a sixth of the screen. It looks like Firefox is purposely trying to fill my entire screen or something. I searched the problem up and the help page told me to change go to about:config and change "layout.css.dpi" to 96. When I did, everything became way too small, especially the webpages: they were nearly half the size they should be. Anyways, there no freaking chance that I'm going to uninstall Vista, so I was wondering if anyone knew and would be able to find the solution to this problem. Because right now, Southperry looks HUGE, and it's totally ridiculous.

P.S. Everything else is normal sized, including IE. And I've set my resolution to make things as small as possible.