When I try to play 4K YouTUbe videos on Firefox, (60FPS to be exact) It lags like crazy, and the CPU usage goes to full. 4K 60 becomes more like 4K 10-20. It is not a network issue, since more video is buffered than played, so I don't have buffering issues. I have a r9 390, but I doubt Firefox uses HA for YouTube anyways. If I download the 4K60 video and play it using Windows Media Player, It plays perfectly at 60FPS. Google Chrome also works fine. It is an issue that I have only with Firefox. I even tried to disable Webm, enable Flash, or change the browser session saving interval, downloading the nightlies, and nothing worked. Is this a bug with Firefox? Do I have to download 4K videos to play them now?