For last few months started to notice that YouTube really sluggish, pages load slowly and every keyboard tap takes long time to register. It was driving me nuts and I blamed FireFox for becoming so slow. To my surprise the Enhancer was actually the root cause! 2 stars because resolution switcher and mouse volume control are very nifty. But this slowdown is unbearable to the point I had to disable this extension. I hope the author will take care of the performance issues.