Actually, I think that this bug may need 2 parts. We've got enough infrastructure for b2g devices (including the emulator) to test this. We might need to add a bit more to test it on desktop. Anyways, we need some way of testing multiple storage areas and verifying that device storage is doing the right things when multiple storage areas are present.
Cleaning up Device Interfaces component, and mass-marking old FxOS bugs as incomplete. If any of these bugs are still valid, please let me know.