Hello Joe.

Make sure you have javascript enabled for YouTube: http://support.mozilla.com/en-US/kb/JavaScript#Enabling_and_disabling_JavaScript

If you have, you may be having a problem with some extension or plugin that is hindering your Firefox's normal behavior. Have you tried disabling all add-ons, except Flash, maybe (just to check), to see if Firefox goes back to normal?

Your above posted list of installed plugins doesn't show the Flash plugin for Firefox. See Flash Plugin - Keep it up to date and troubleshoot problems and Install the Flash plugin to view videos, animations and games

You can get the Flash Player here: http://get.adobe.com/flashplayer/otherversions/ (Adobe Flash Player) "Select operating system" and make sure that you get the "Browser: Firefox, Safari, Opera" version. Make sure that you remove any check mark to install additional software (Free McAfee Security Scan (optional))