If the ONLY thing your product has to offer over the competition is your personal definition of "open" then YOU WILL LOSE, because nobody cares about your definition of "open" when your product is inferior in every.single.way. when compared to the other choices.
Apple has the walled garden which offers a unified user experience, Android has the app support and wide choice of devices your apps will run on, even MSFT has an advantage in the "bang for the buck" of their quite affordable offerings and the ability to integrate it into your Windows 10 desktop...what does FXOS have? It has Mozilla's definition of "open" which last I checked doesn't even jive with the GPL version of the same word...yep, not got a chance.
We have seen this time and time again, from "open" phones to "open" game consoles to "open" tablets and in every case? The results are the same, either death or usage numbers so low as to be below the margin for error. FXOS will peter out, the slow death of fading relevance and lack of support because of the simple fact that it has nothing to offer the consumer other than the Moz definition of "open".