This is not the first time this happened. Some months ago (or years even?) I had the same behavior which either eventually stopped, or I figured out which setting to toggle to make it stop semi-permanently. Unfortunately, I don't remember what that setting was, and I no longer care enough to spend the time to search for it.

When it becomes less effort to create an account on a forum, type up a message like this, and migrate to a new browser, you lose. I hung on with this browser for as long as I could. I get it, you have to pay the bills - but when you make it difficult or impossible to remove the advertisement, I'm gone.