State in background scripts, synchronously available across restarts

[Rob--W]

During TPAC 2024 (#659), we discussed the topic “there is not a good way to bootstrap state in the listener” in the context of background scripts. The outcome of the discussion is that we need an API that enables extension to store some state that persists across background restarts. Some limited amount of data may even be available across browser restarts. The exact details have to be figured out in a proposal.

Note: the request for state to be available at the top level has been requested before, in the context of content scripts, "globalParams" (#536). The request here is independent of that, and should not be confused with it.