For heaven's sake, man, turn it off. You'll never be able to actually use all six cores at 100 percent if you browse using hardware acceleration. You paid for those cores-- and now they're going to sit idle while your video card offers to do the "hard work" of decoding a video stream? That's insulting, that's what it is.
People who don't wish to push their computers to the limit will usually advise leaving it on, and only switching it off to resolve strange and buggy behavior.