Firefox and Chrome are application platforms, like your OS. It doesn't make sense to count them. They don't only run youtube, unlike VLC which is only a media player. Otherwise VLC counts as 20 GB (or whatever) for the OS as well.
Because then you have the 7GB OS + 95MB Firefox + 100kB YouTube vs. the 7GB OS + 30MB VLC + 2MB youtube-dl
And, additionally, the browser is just a document displayer, like a PDF viewer, or an image viewer. 135MB for that is far too much in any case.