Did YouTube’s compression change for desktop? Maybe a Linux issue?

All of a sudden, I'm getting these wicked compression artifacts all over the place, often showing up as a clear divide across the centre of the screen, but also sometimes bleeding over. I thought it might be a Firefox thing, but it persists across browsers. It doesn't happen on mobile as far as I can tell, so maybe it's a new Linux bug? I dunno, I just thought I'd ask to see if anybody else has had issues.