I just carefully re-read the text, and it never quite claims this is a security issue with Firefox. (I did not watch the video, so if it's in there, I did not see it.) It just says a lot of various true things, and leaves the implication hanging in the reader's mind without addressing it. I agree that it would be improved if the author was more clear that this is just the way of things in our current user-based permission model and there isn't anything Firefox can do to truly stop this.

As a factual presentation, it is worth pointing out to interested people that Firefox's protection is only advisory, and not completely perfect.