Rated 5 out of 5 stars
Works great on the current Yahoo Mail. However, I'm using the Beta version of the new Yahoo Mail and it doesn't really work on that. The right ad panel is sometimes hidden (but the space still shows) and sometimes isn't, while the top ad panel shows all the time. However, I would imagine that once the new version of Yahoo Mail goes wide, there will be an appropriate update to the add-on.
Yes, I have not yet received an invitation/indication of the new Beta mail yet (in fact I was not aware they have introduced a beta). Whenever that happens, I'll try my best to fix that soon.