In http://groups.google.com/group/mozilla.dev.webapi/browse_thread/thread/db29059c5c8e2527/96f895f4c49593c4 there was a discussion about an 'Homescreen' API. Basically this API is a way to send back and forth information between the main application of the B2G front-end and the chrome running this front-end. (The API is called 'Homescreen API' but the name does not make sense in a world where the homescreen is a distinct application from the application that manage application windows - like in Gaia). This is probably hard to draft a correct API at this point since the needs change over time and the API should be avoided as much as possible (imo).