Which is a UX issue, not a Web standards issue. None of the major forks were made due to a difference opinion about how the standards should be implemented, so they are all dependent on Mozilla to implement the standards.
I suppose, but I wouldn't try to predict the response to Firefox becoming unmaintained and interested parties who might step up to carry the torch before it actually happens. It's the primary browser of the largest three commercial Linux distros.
Which is a UX issue, not a Web standards issue. None of the major forks were made due to a difference opinion about how the standards should be implemented, so they are all dependent on Mozilla to implement the standards.