I'll look into some threeJS demos to see how it goes (ex. https://bruno-simon.com/ ). Are there any other specific JS demos you've had a bad experience with?
Another example is iD[0] Editor on https://www.openstreetmap.org/. But there, to be fair, it's also slow on Chrome but I feel it's a bit slower on Firefox.
Oh man this was a rough one both for FF and Chrome but Chrome did perform better slightly on cursory glance.
Thanks for providing these links, they're definitely a good rule of thumb benchmarks to test new browsers
So far, I haven't found much of a difference in performance of websites but it's still early times for me.