The version number almost says it all. How can you get excited about a new Firefox release with any feature, when it's just another rapid release. It could have true hard AI and no one would notice any more. It would get lost in the staggeringly mediocre array of non-features nobody wants, forced UI changes, broken addons, and developers that decide they know more about what people want than the users do.
Firefox adopted Google's rapid release cycle on a project that it was neither technically nor culturally suited for. One has to actually admire their dogged persistence to holding course in the face of what is an almost a completely unified chorus of "WHAT THE FUCK PEOPLE?!?!?".
I recommend Palemoon. A fork of the previous Firefox LTR, it has refused to add features unless they make sense, is compatible with most addons, and has its own growing body of its own addon developers that are quite loyal to the project for the simple reason that the project remains loyal to them. That's not to say that it's a static browser. Just one that took the best of what Firefox was and decided to continue in the direction of sensible goals and not alienating its user base.