Apple didn't even build a browser from scratch. They took Konqueror's KHTML engine, then built Webkit with it.
We could do the same with Firefox. As the matter of fact, there are already forks out there, like IceWeasel, Librewolf, Pale Moon, etc.
What's going to happen is that one of those will start raising to the top. That's exactly what happened with Firefox. Mozilla had the Netscape suite, open sourced it, then fucked it up. When it fucked it up, I decided to try one of the alternatives, Phoenix in this case. Then Mozilla decided to drop the Netscape Suite and adopted Phoenix, which eventually became Mozilla Firebird, and finally Firefox.
For me chrome just worked better (Mac) but since adblock is mandatory for me I switched. Afraid that if ff will implement AI my experience will be even worse.