@rlmcneary2 @pluralistic There was a similar case with BT in the 2000s, they inserted their own adverts into web pages when serving them to UK customers. I noticed when they did it to my own site. They got a stern letter about copyright infringement, which it was, and swiftly dropped the idea.
The difference here is that the webpage is delivered directly to the user's machine, and the user then chooses how to modify the data.