I can't believe I've just read this when Mozilla get so much of their money from Google.
My personal prediction is that the same problems will emerge with privacy on this device as have emerged on the web and in the app space. The market becomes overly saturated with products, there's a price crash and eventually people expect apps for free. Then the most successful apps will be made free and monetised by harvesting data from their users, if not through Mozilla or the OS then through direct tracking through the app, sent to the vendor. Users may be able to pick apps that work with their choice of privacy settings, but the mainstream mass market won't care enough to bother.
As with my much-derided comment about using HTML 5, I don't see this as a new model in any way, and it contains all the same flaws as any other software market that have led us to the situation we're in today.