But some slowdowns are not infections. Just a few months ago Firefox was a slug. I reset Firefox and all better. While it would have be fun to track down what that was, I didn't have the time at the moment.

Try another user account too. Grif writes:
"If you can download the tools listed below on the problem computer, great, but you may need to use a separate, clean computer, download the tools, copy them to a DIFFERENT flash drive or CD, then transfer them to the infected computer."

I use Grif's list a lot. Great advice,