With firefox, you can see the ads that pay for hosting that content you are interested before, during and after you see it. I don't know how enforceable is that you should watch some content exclusively with the provided frontend, but it really makes a difference for them how you watch it.
And you see that in the downloaded version as well whenever it is part of the video. The fact that youtube implemented this differently for some of their ads is their problem, not mine.
That is like complaining that you aren't allowed to view a webpage on a kindle because the ads are supposed to be viewed in color.
