Greasemonkey was wonderful back in the day.

The amount of use agency, the ability to tinker, to not have to put up with a one-size-fits-all app experience, but to be able to customize it to work for you.

It had amazing generative potential of an ecosystem that was self-catalyzing.

But Greasemonkey ultimately had a low ceiling due to its security model.

The laws of physics of a system, its security model, sets both the speed of distribution and also the ceiling of max penetration.

Imagine a Greasemonkey for the post-app era that didn't have such a low ceiling.