This page is very broken for me (Firefox on Android). It looks there's some kind of Z-fighting happening on the buttons? Also, they scroll slightly faster than the rest of the page, such that when at the bottom they're completely out of their sockets.
But the intense latency and low framerate feel makes it nearly unusable for me I'm afraid. And I'm trying on a powerful workstation. There are some fundamental performance issues in this implementation.
I could see it being intentional too, to add a sensation of weight? If that's the case, that's a good idea, but the current implementation feels more laggy than weighty.