How to Fix Annoying YouTube Jumpiness in Firefox - Firefox - Lifehacker
http://lifehacker.com/5342636/how-to-fix-annoying-youtube-jumpiness-in-firefox
"Ever notice an annoying, persistent lag every ten seconds or so when you're watching a YouTube (or other) video in Firefox? Reader Bernard Sandberg has, and he's written in with a smart about:config that solves the problem for him."