I was working on a carousel library a few months ago. I had made a few stress-test demos so that I could catch obvious issues while I was adding things and tweaking things. One carousel there had 16K slides. On Windows both Chrome and Firefox managed that fine. They scrolled from start to end and back without issue and you could see, I think, all the frames in my 60Hz screen. On GNOME and X11 (dual boot, so same hard…
Firefox remains very conservative on enabling modern features on X11. Some distributions force them on, but otherwise it's up to the user to figure out how to do that. It's likely that some hwaccel flag in about:config wasn't turned on by default. Similarly, if you want smooth touchpad scrolling, you need to set MOZ_USE_XINPUT2
So old school throthling if you don't use the "right" version (Apple batterygate, Microsoft wordperfectgate). They could blame it on testing though (we only use Wayland and we are too lazy to test the X11 version)