I’ve done some experiments by modifying the “session-state” example
add-on. It appears that values set with sessions.setWindowValue do
indeed persist across browser restarts. That’s good
news! And all I need for an add-on I’m working on.
For anyone curious about tabs: For sessions.setTabValue the values were
persisted across restarts in most cases, but the borderify border wasn’t
appearing after restart in one of the open tabs. The tab was an
active/focused tab (the only one when one window was open, and one of
the active/focused tabs when several windows were open).