Firefox is irrelevant with a marketshare of 7% and it's not needed. What is needed is a true competitor for Chrome not a long forgotten fever dream.
If such a competitor were to use Chromium/Blink, how do they differentiate from the other browsers? How do they avoid changes that Google push into Chromium/Blink that they don't want? Where do they get the resources to develop standards they want to support like MathML or several of the CSS drafts?
If such a competitor were to create their own web stack, where do they get the resources and time to build the HTML, CSS, and JavaScript to a level that is competitive?