The one type of in-page modification they used to do is that they would add a "tip" button to the content creator of some social networks like Twitter or reddit. That had nothing to do with "replacing ads" though.
> replaces an ad, they put the new ad in a popup
Incorrect. There is no 1:1 replacement. You as the user can define how often you want to receive notifications, and even then the notifications only come when you are switching context between any action. It won't interrupt you while you are watching a video, working on google doc spreadsheet or reading though HN.
click on it, your horizon might be broadened by the added knowledge.
lalaland1125 is making claims about what they actually did, and those claims are not correct.