From a pragmatic perspective, the fewer browsers we as developers need to support, the better. There has never been any meaningful standardization between browsers. Even "modern" browsers are all different enough that you need to test and code specific paths for each of them unless you stick to trivial things.
Personally, I want the same thing I wanted back in 1996 when I started this ride: One browser to win, and the others to drop to such a tiny share that we don't need to support them anymore.
Firefox performed a service in convincing Microsoft to update IE6. But that was fifteen years ago. Since then, Chrome has arrived and demonstrated that it is far and away the best. In my opinion, Firefox would serve us best by simply stepping aside. All it does today is force us to code yet another path into everything we build.