[bberenberg]

It works fine in another browser. So I don't think it is a hardware issue? Is there a situation where Chrome/Vivaldi would be able to use hardware the FF wouldn't? And 90% of my time is spent on power (top left usb-c port).

[DavideNL]

Using a different browser results in a different video (/codec) being downloaded. The different codec is what can cause your hardware/cpu to spike.