To differentiate, one idea is that Firefox create optional browser extensions to support local mesh networking over wifi or bluetooth and a container or VM for hosting servers as a safer and more portable alternative to native appstores. This would represent a step back from the FirefoxOS notion, but a step forward from the browser, and could drive interesting proximity applications as well as gaming, which could lead to new users and properly challenge the status quo.
Rationale: Mobile device vendors are too heavily wed to the cellular carriers and related regulatory inertia to do anything here. In particular, carriers are also major distribution channels for a lot of mobile devices, creating a resistance to anything but carrier-enabled mobile-data as a frontline topology.