This is grounded in the assertion that a website’s HTML/CSS is a protected computer program that an ad blocker intervenes in the in-memory execution structures (DOM, CSSOM, rendering tree), this constituting unlawful reproduction and modification.

“There are many reasons, in addition to ad blocking, that users might want their browser or a browser extension to alter a webpage,” Nazer says, explaining that some causes could stem from the need "to improve accessibility, to evaluate accessibility, or to protect privacy."

Stylus and Greasemonkey would presumably violate that, for example.