I wonder how long it will be before Mozilla are in real danger of losing control of the browser they call Firefox, if they continue on their recent trajectory. We're talking about Open Source here, so it is always possible to fork it under different branding, and a few groups already have for one reason or another.
Of course, in reality, forking and then establishing the fork as a mainstream replacement that aligns more closely with the traditional advantages of Firefox would be a huge undertaking. For any new browser to gain traction outside of geek communities would surely require both a substantial user base and substantial support from the development community.
But it's been done before, even for large and high profile projects, when the existing corporate stewardship wasn't getting the job done: the LibreOffice/OpenOffice split is the first example that comes to mind. If I were this week's CEO at Mozilla, I would consider a mainstream fork to be at least a plausible threat by now.