User Agent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:85.0) Gecko/20100101 Firefox/85.0

Steps to reproduce:

Visit https://unanim.studio and try scrolling that page

Actual results:

This website is the most bloated website I've ever seen, and Firefox takes an absolute beating with it. I think it would be valuable for you folks to archive that website (for posterity) and integrate it into your performance test suite benchmarks, because Firefox slows to a crawl and only manages what feels like 3 to 5 frames per second on this site... whereas Chromium feels closer to 20-25 fps. I believe that this website being particularly good at exhibiting the worst performance issues, if you can optimize at least some of them, you will 1) see the difference clearly 2) the whole browser will speed up on other websites as well.

Expected results:

Somewhat smooth/fluid scrolling and animations. Chrome/Chromium manages to handle that site pretty smoothly (which was, I can guess, only designed for Chrome), maybe at 24-30 fps or so, which is still better than the 3-5 fps you get with Firefox.

The Bugbug bot thinks this bug should belong to the 'Core::Graphics' component, and is moving the bug to that component. Please revert this change in case you think the bot is wrong.

Profile shows that most of the time is spent animating radial gradients on the big background 2D canvas. Using WebGL or CSS animations would probably fix this.