Competition, especially enough competition to start affecting prices in any meaningful way, doesn't just happen because alternatives merely exist.
The alternatives need to be extremely compelling in order to draw users away from very well-established incumbents.
From what we've seen so far, it's very doubtful that Firefox OS is capable of doing this. In terms of functionality, it is far behind what other mobile OSes have offered for years. What's worse, what it does offer is already offered by its competitors. It also offers much less flexibility when it comes to how developers can build their apps. It doesn't really compete in terms of cost, as used Android and iOS devices are widely available at very reasonable prices, even in developing nations. Finally, the claims about it being more "open" are specious, at best.
It's very difficult to find anything compelling about it. Regardless of what criteria is considered, it just doesn't offer any advantages. Widespread uptake just does not happen when this is the case.
It could be argued that the alternative for the FirefoxOS devices that have been announced are Android devices with similar hardware, but running either outdated versions of Android or suffering the limitations of running a platform built for newer devices on a device with more limitations.
This is a similar position to the one Microsoft is taking with WP7 through the less expense carriers in the US, the speed and responsiveness of WP7 is put up against Android 2.3 on a low capability CPU and GPU. WP7 seems to have been designed to render the "tile" display fast on lower quality graphics hardware.
If Mozilla and partners are positioning these devices against entry level devices from companies like Motorola and ZTE in less developed countries they could do well.
The alternatives need to be extremely compelling in order to draw users away from very well-established incumbents.
From what we've seen so far, it's very doubtful that Firefox OS is capable of doing this. In terms of functionality, it is far behind what other mobile OSes have offered for years. What's worse, what it does offer is already offered by its competitors. It also offers much less flexibility when it comes to how developers can build their apps. It doesn't really compete in terms of cost, as used Android and iOS devices are widely available at very reasonable prices, even in developing nations. Finally, the claims about it being more "open" are specious, at best.
It's very difficult to find anything compelling about it. Regardless of what criteria is considered, it just doesn't offer any advantages. Widespread uptake just does not happen when this is the case.