The flurry of articles portray the Mozilla Firefox 'operating system' as a contender against Android OS phones, helping to push them down in price to sub $100. That is a stretch of reality... probably fed by hype from the Mozilla Firefox camp.
Another shift is happening: while the browser has become part of a more diverse environment it has also become more powerful. HTML-5, leaner scripting including display frameworks such as Twitter Bootstrap, and the growth of rapid development platforms including applications development and web CMS has enabled the browser to do more as part of a distributed, software defined network experience.
The outcome of this is probably that browsers will become less important of a factor in determining price, rather than more. The cost is shifting down across all the web browsers and OS environments, except, arguably Apple's OSX because of the control the company places on their platform.
meanwhile, device suppliers are struggling for ways to differentiate themselves while jumping from one frying pan into another: handset suppliers are forced to use one or more of the OS environments while leaving subscribers open to making use of their choice of browser and applications and content stores. They do not want to become captive to a single OS platform supplier.. thus the willingness to support alternatives.
I suspect that Firefox will be similar to Microsoft OS.. its likely to capture a small portion of marketshare. The difficulty is overcoming the large development groups that support Apple, Google Android/Chrome. This goes beyond the OS itself into apps and content stores, services support, and marketshare momentum. While the situation remains fluid, its unlikely that Mozilla Firefox will claim a large part of the device OS share.
What does this mean for Sprint-Softbank? practically nothing. Like other operators, they can play off the different environments but will support those that subscribers most want.