Yes, but for now, it works just fine. Much better than Chrome IMO in fact. As long as Mozilla gets enough funding to continue development, this shouldn't change.

>Linux accounts for somewhere between 0.5% and 3% of the desktop OS market, depending on who you ask.

Why does this matter? It works fine for countless people and companies. I'm using it at work right now, and have been using it exclusively at work for many years. Marketshare is meaningless with Linux anyway because almost no one pays for it, so of course it doesn't show up in marketshare surveys.

>Mastodon, Diaspora, Lemmy etc. are niche products used by far fewer than 1% of people.

But they exist and work. If people don't like Facebook et al, they're free to switch, and they have no right to complain.

>Competition doesn't simply mean "other stuff exists".

Yes, it really does. Those things are all viable alternatives. That's the definition of competition.