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.
The effect indicates to users who may not have scroll bars enabled that a box can be scrolled. The fade should be removed when a box can’t be scrolled in that direction.
CSS effects tend (tend) to be faster and conceptually is a better place for effects anyway.
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.