works in pretty much all browers excepting firefox which doesn't have CSS scroll animations yet, but the nightly version does, so it should be generally available soon.

demo site: https://pete.design/tw-fade

github: https://github.com/petekp/tw-fade

npmjs: https://www.npmjs.com/package/tw-fade

if you use it i'd love to hear how it goes and if you have any feedback.

I don't know if this page is a demonstration of your plugin, I'm guessing yes but I can't see any masking going on, it seems to scroll just like a normal page but much more laggy.

EDIT: Oh I see in your comment now, it doesn't work in Firefox. My mistake.