When I went to watch a youtube video in Safari the page loaded but the video player was not working. Instead of the flash player it was just a black box.

iTunes was running and when I pressed the volume button on my keyboard my songs started to corrupt. My Mac also seemed to start slowing down, ie. in Safari the scrolling was horrid and nowhere near smooth.

Is it because I enabled an extension into Safari called, "A Cleaner Youtube"? (I tried turning extensions off, then restarting Safari but the same problems occurred when I tried to load another youtube video)