No, it's not. Mozilla has 750 employees (not all of whom work on the browser, but still) and hundreds of millions of dollars and they're constantly struggling to keep up with Chrome. 9 part-time devs cannot do this.
Look at the following browsers: Otter Browser Min Qutebrowser Links Basalisk Surf Bromite (only has 7 contributers)
It is possible. Of course it's possible. Just depends if that situation were ever to occur, whether people would become passionate about that project
Basilisk and its sibling Pale Moon are an example of how hard a fork is (both being pre-Quantum Firefox); features removed because cannot be maintained, incompatibilities, poor performance and many vulnerabilities.