Some kind of (virus?) has attached to my Firefox and keeps changing my default search engine to Yahoo. I've run several antivirus programs to no avail. Frustrated, I tried to uninstall Firefox... but nothing happens when I click uninstall in Control Panel. Any ideas?
You should take a look at the Knowledge Base article Use the Search bar in Firefox. Your default search might have been changed by a particular site. Sites like MSN, Yahoo, etc have been know to ask to become your homepage and change your search engine.
Start Firefox in Troubleshoot Firefox issues using Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).
Don't make any changes on the Safe mode start window.