When it comes to any of the major browsers I really doubt power users drive any significant market share. But is it the same for a niche browser? Mozilla have been trying to chase shiny features to drive adoption yet they somehow keep losing more and more market share. Why can't they at least listen to some of the people who are actively trying to use their browser... have they decided they're going all in and they'll either have it their way or they'll die trying? I would be really sad to lose my favourite browser like that.
My guess is that power users are picky and opinionated. If one of their favorite features gets cut back or dropped they may loudly complain on the way out.
Mainstream users don't care about any of it. The only reason Firefox or even Netscape were ever mainstream was because they were undeniably better than alternatives. User advocates got the word out, but it was the clear advantages carried the day.
Now that browsers are all mostly the same for the laymen there's no reason to change the default. Or if they change it's only to whatever's most familiar.
