Welcome! If you’re reading this document, it means that you have volunteered (or have been volunteered) to implement a client implementation of the messages feature of Firefox Accounts.
First of all, what is this new feature? Also referred as “Pushbox” (our back-end server implementation), FxA messages is a way to send durable data payloads between devices registered on the same Firefox Account. The reasons we have started this project are stated here (be careful, a lot of API specifications are outdated!).
As for now, FxA messages are only used as the new backbone of "Send Tab". However, some other teams have expressed interest in our platform to send data quickly between devices.