Making a browser is Mozilla’s purpose. If Mozilla can’t do that, it doesn’t have a reason to exist and will fail. If the Feed the Children charity decides that feeding children is too hard and decides to water plants instead, I expect it will fail too.
The Mozilla Manifesto says nothing about web browsers. If you think they should throw it out and focus on making web browsers (and abandon their mission as an organization) you'll have to take it up with them I guess.
Well, 99% of "the Internet" is the web, so a free web browser is the vital part in that. And not some tool about "remixing HTML" or open badges or something [1]
With mobile native apps, there's no way that 99% of the internet is the web. Video accounts for 60% of total web traffic, and a good chunk of that is not through a web browser, I'd imagine.
That's why they've tried in the past (and hopefully continue to do so) to provide resources like you're pointing at to "the public" to build and create their own special place on the Internet. Something outside the gated ecosystems of those big internet companies (Facebook, Twitter, etc).
Have they gotten it perfectly right every time? No, but that's okay, and it's good that they're even trying because not that many people (or companies) are.
