Mozilla very consciously uses the term "the web" because it evokes the right things in the minds of their target audiences: developers and end users. It has a sense that everything works together like "normal" web content. You don't have your videos stuck in an embeded plugin rectangle. You can control playback of audio with JS. Mozilla doesn't want you to look at a phone and think "I can run Firefox on that" because no one cares. They want you to think "I can use the whole web on this" because that's much more interesting.