Pretty much is though. For Google not to impose its will on the internet as a whole, there needs to be meaningful competition. Firefox, for whatever reason, went from a browser capable of influencing policy to a niche browser for nerds, myself included.
So yes, the future of accessibility is very much a popularity contest and Chromium is sitting pretty with 70+% of the votes.
MySpace still exists. You can still log into Myspace and use it. Same is true of Livejournal, ICQ (last I checked,) and many other bygone services.
They're not going anywhere either. But they're still useless outside of edge cases.
I want Firefox to succeed. But I've also been watching it lose relevance for the last 10 years. I'd prefer it not to go the way of MySpace because its users are too stubborn to admit that it has a problem.