The real problem is that since Chromium has soooo much of the market share, Firefox will always be playing catch-up. If Google decides to go full rogue and ignore W3C specs entirely and make up a bunch of their own shit, that devs then start to use because why not since the majority of their userbase use a chromium based browser, then Firefox can easily be taken out.

That was exactly what the .NET family of languages was back in the day. Still is, I guess? You could write in VB, C#, or F#, make use of the same standard library and general principles, but then it would all get compiled to the same IL code in the end.