I agree with you that ads are good for the internet, but I'd very rapidly put myself against the idea of any legal issue with modifying a website on the client.

I agree with you that ads are good for the internet, but I'd very rapidly put myself against the idea of any legal issue with modifying a website on the client. There should be no question that I can do what I like with the HTML served while it remains on my machine - whether that's blocking a popup, removing an annoying advert or terribly placed menu from the DOM or anything else.