Ask HN: Is there an accepted name for writing browser-based user scripts?

The type of development I mean is GreaseMonkey or TamperMonkey scripts -- or even browser plugins -- that modify and "hack" web pages after they've loaded in the browser.

Is there a name to refer to this type of thing? Is this an accepted or pseudo-discipline? I'm trying to find best practices around this, but it's hard when there doesn't seem to be a nomenclature around it.