It looks good in a maximized window on an external retina display on my MBP.

One thing, though, is that it "stutters" every 15 seconds or so. Like, it pauses for a noticeable time, like hundreds of ms. The UI shows a consistent 119-120 FPS, even when this is happening.

It's possible the fault is Firefox, and not your page. I do have 64 GB of RAM, but also a zillion tabs open.