BlackBerry OS and Windows Phone, which are nearly irrelevant compared to Android and iOS, are absolutely huge compared to Firefox OS, Tizen, and the other mobile OSes.
Firefox OS and Tizen will have absolutely no impact on Android.
There's also the theory that Samsung will probably want to stop being dependent on Google, and use its own OS. That could be a game changer.
Mozilla is leveraging a large existing developer base and relying on the brand power and capabilities of Firefox that they have full control over. Their choice of market is interesting too, as it seems to be largely served by low-cost hardware stuck with outdated Android installs with no upgrade paths on the horizon. Meanwhile, Google is distancing itself from Android as a product and instead pushing own devices as "the" Android experience, leaving the low-cost hardware market with stale software.
These seem like thought-out strategic moves Mozilla is capable of pulling. It'll be interesting to see how things play out.
Not that I think either will really take off.