That being platform control and advertising.

Google advertises chrome with it's services and is the incumbent. It's also preloaded and unremovable on Android.

Microsoft advertises edgium on Windows and makes it unremovable.

Apple only allows webkit and safari clones on their platform.

Firefox even if it's the best browser in the world would have the same problem that Linux has. Namely that Linux may be better and fit the needs, but people aren't going to bother installing it. Just look at Windows 10 and how many people are pissed at various aspects from telemetry, updates, ads and still these same people can't be bothered to flash Linux. Linux has something like 1-2% of the desktop market.

The other issue with (2) is that R&D into Firefox will not return money. Not unless they choose to basically switch to blink and offload the R&D costs onto Google. Heck Microsoft themselves did the same because they realized the R&D costs weren't worth it.

If Mozilla wants to stay alive, it needs to diversify and find a niche not dominated/controlled by Google, Microsoft and Apple.