Youtube playing extremly slowly in Firefox on OpenSuse TW

I installed a fresh OpenSuse TW system on my machine, and everything went flawlessly, except for YouTube. I installed the codecs with opi codecs; I enabled/disabled hardware acceleration and enabled/disabled media.hardware-video-decoding.force-enabled; I enabled/disabled layers.acceleration.force-enabled; I enabled/disabled gfx.webrender.all; None of these solutions worked.