None of that matters. That is not why people are not installing Firefox. It is because Google tries to force Chrome on all their devices and sites, and Microsoft tries to force Edge on all their devices and sites.
Most users don't even realize they have a choice for browsers or what the choices are and why. And in corporate settings, users have no choice. "Power users", as you mention, are the way less than 1%. And most Firefox users are not passionate about the theme (and yes, I do care, and use css hacks) or that occasionally the icons or tab design changes (LIKE IT DOES IN ALL OTHER BROWSERS TOO).
Firefox has been and will probably remain better than Edge and Chrome in many aspects. But users don't care about open standards, privacy, ecosystem security, best ad blocking options, most configurability, etc. They use what the machine came with, or what some site said "works best in" or some idiot tech support place says "we support only."