The system messages API waits for the app registry to be ready, and buffers messages sent while it is not ready. broadcastMessage() also uses this buffering. This is fine in the case of an app-only web runtime where all apps will be ready only after the registry is ready. For firefox desktop, where we would like certain APIs and their corresponding system messages to be available to web pages, this prevents the use of broadcastMessage(). broadcastMessage() should be modified so that web pages registered for system messages immediately get broadcast messages, while broadcastMessage() still buffers messages for apps. There isn't a use case on desktop right now for broadcastMessage(), but this should be fixed for an API that requires it.

The intention is to move away from system messages for IPC on desktop. Currently push uses the message managers.