Firefox is open source and it doesn't need to be tied to Mozilla. Maybe a fork is necessary.
And there also is a fork of XUL-era Firefox already, called Pale Moon, which various people have declared will soon be unusable with the modern web because there aren't enough people that care about it enough to implement Web Components, to the point where the Pale Moon developers were asking websites to not implement Web Components[1]. Are the developers of those websites going to pay attention to a couple of developers maintaining their own Firefox fork that much less people use than standard Firefox? (And we're talking about Firefox, which itself has a single-digit market share.) That on top of the implications of security exploits being found in such a massive codebase faster than the development team can patch them, given how many features are being added to web standards so quickly, probably with the expectation that companies like Google or Mozilla already have the developer capacity to implement them on a set timeline. There's simply so much source code to maintain, and adding the new features that the modern web is going to require to be usable in a few years on top of maintenance takes a significant amount of effort.
The only way that a program as complicated as Firefox can continue to be improved and used by enough people to be viable is if it gets worked on by people with enough time, and I believe that's only practical if people are spending that time working on Firefox because they're salaried. Yes, that's partially because web standards are constantly expanding in scope and complexity, and I'm not really sure what we can do about the complexity creating a hard dependency on Mozilla continuing to exist because, unlike the source code of Firefox, the forces driving those standards are out of the reach of the average OSS developer.
Mozilla has certainly done a lot over the past decade that effectively guarantees that neither Firefox nor Gecko can realistically exist without the continued existence of the Corporation.
Blink (Chrome's engine) was once KHTML. KHTML was maintained entirely by volunteers, so I think it's entirely possible for a team of volunteers to maintain a web rendering engine.
I think most people severely underestimate how much of a modern web browser is code that does things completely unrelated to rendering web content (think telemetry and the like ,etc). Now, telemetry also needs a backend to send data to, and servers to run that backend on.
My point is that many of the people that work on a modern browser are working on things that are unrelated to rendering web content, so their equivalent would not be needed in a volunteer team. You don't need any admins to administer the servers that run the telemetry backend services if you don't have any telemetry in your browser.
It is very, very okay that ubiquitous and greatly loved projects do one or two things well.
And even if this better-will project is formed, and funded, and worked, there is nothing stopping the team from picking up all the bait-and-switch, corporate speak, etc., when they are wearing the same shoes as Mozilla.
In any rate, it's not as simple as someone with better-will to fork the project. I'd rather stay with Mozilla for now, because 1) they are a public entity who cannot commit an evil deed and simply ghost everyone, so they have the motivation to not be hated too much, and 2) they are the only player other than Webkit family and the Chromium family on the browser market, while nobody else has the power to even enter the competition (at least for now).