It says its using the GPU but if you look at the cpu time required to play a 1080p video within firefox vs playing the same video with mpv

www.mpv.io : a lightweight player that among other things can transparently stream any url understood by youtube-dl

It uses 20x as much cpu as mpv. For purposes of comparison this is like Toyota selling a car that goes just as fast as your Ford so long as you are OK with only getting 4MPG.

There is an addon if you prefer to right click on a url and open in mpv or in an addon like Tridactyl you can do the same with your keyboard. It also lets you speed up and slow down the playback speed which is nice for speakers who talk too slow and take a while to get to the point.