I removed Firefox and then re-downloaded it. It's better, although I still have issues with some sites. Even as I type this, I can see the tab indicate that it is loading this page and the page (tab) that preceded it. It's like it never fully finishes loading a page. The green bar on the bottom right is never quite full.

I use an antivirus and two spyware detectors on a regular basis and don't seem to have anything weird going on. As much as I dislike Vista, the PC that runs on that system using the very same build of Firefox loads pages very quickly and with zero problems.