Earlier quoted context omitted.
GPU acceleration is not a magic bullet it seems. In our case drawing large SVGs suddenly becomes really slow when GPU rasterization is enabled. Chrome has the same problem. I really hope we will see more polishing in this area and maybe a cooperation between Chrome and Firefox developers?
Thing is, when I play the same video with VLC which uses HW decoding, it doesn't even break a sweat. So I think there might be something wrong on the browser part...
I'm also experiencing FAN noise raise on my Ryzen APU based laptop.