Earlier quoted context omitted.
You have to scroll all the way through the page to activate all the gimmicks. Then it never stops, and loads 2.5 cores permanently to 100%, which makes CPU fan spin to the max.
Oh my god, that's hilarious. I was wondering why my lap was warm all of a sudden. Htop said firefox was the culprit so I closed out all my tabs except this one. Then I read your comment, opened the page, and scrolled all the way to the bottom—my cpu temp just steadily rose till it throttled. All the animations are smooth, though. Note: I'm typing this from a 9 year old thin-and-light, so that's probably part of the p…
Fixing it should be as easy as disabling the animation that's outside the viewport, I guess.