It's literally what the extension does and what it's for.

It's a bit weird to call intended functionality for sonething you install explicitly for that purpose an "ad". Let alone an "obnoxious" one.

I mean, how else would you expect "email protection in the browser" to work at an extension level, other than the extension trigerring a message with more information when you're about to type your email?

I think I should clarify that I installed this extension quite a long time ago ago, and it has never served an unsolicited inline notification to me of any kind. The stated purpose at the time was website tracking protection, similar to something like PrivacyBadger, and that's what I use it for. It added a small button to my extensions menu that I can click to see some information about the website's requests and turn tracking protection on or off. The behavior I am criticizing in this post is not what the extension was for when I installed it, and it's not something it's ever done before.

I think it would be reasonable to notify me about this new feature in a less disruptive way, like from the extension's existing information pane. Inserting that inline into the websites I use isn't the only way to notify me, but it does seem like the most obnoxious way to do that.