I don't want to be negative about this, but TBH I can't think of a webpage -besides Wikipedia- that will work fine restricting non-free JS.

At this point I can't put my faith in web authors, since they could not even take care of prefixing the CSS for non-webkit browsers (not trying to fault the web authors, but trying to point out that prefixes were a less-from-ideal solution that ended up in the -webkit-disaster)... How can I expect from them to license their code with a free license?

On the other side, the awful practices (like using JS for animation, or tightly coupling the site code with the Tracking code) exists in most websites (including mainstream ones).