I haven't been able to test this as my test device is too old. But, I'm betting my money on Firefox somehow rendering `background-attachment: fixed` differently from Webkit/Blink which is causing the slowdown.

I'm looking at switching to GPU accelerated transforms instead but that brings a couple of new challenges.

It's a lot slower in Firefox, but I find the effect looks nicer in Firefox (if you ignore the lag). The rendering is faster in Chrome, but the effect appears much more subdued to me.

Nuts, that doesn't sound good, I haven't been able to test on Android because my Android device does not have a Gyroscope :\ Hope to fix this next week.

Same. Firefox on pixel 2 renders about every second. Chrome works

Same here. Sort of works, but very laggy. Firefox on OnePlus 3T.