Aren't we also moving toward not even letting cross-origin scripts having very little access to information about the page? I read some stuff a couple years ago that gave me a very strong impression that running 3rd party scripts was quickly becoming an evolutionary dead end.
Definitely for browser extensions. It's become more difficult with needing to set up CORS, but like with most things that are difficult, you end up with developers that "open the floodgates" and allow as much as possible to get the job done without understanding the implications.
