Browser.sessionstore.resume session once
From MozillaZine Knowledge Base
Firefox 2.0 introduces a built-in Session Restore feature, allowing the user to continue browsing from where they left off if browser restarts. This preference controls whether the last saved session is restored once the next time the browser starts (for use after software updates, extension installation, etc.).
Possible values and their effects
Restore the previous session when the browser starts next, but not again. Set the preference back to false upon session restoration.
Do not restore the previous session. (Default)
First checked in
Has an effect in