I have a pretty bad habit of letting my sessions go on for ages - multiple windows, multiple tabs in each, have had literally hundreds open at different points, but never had an issue with restoring the session if the browser/computer crashed.

Today I opened Firefox and got the usual restore screen, but when I selected Restore I got a session that was from weeks, maybe months ago. Checked my history and it's all up to date as of yesterday, nothing missing in recently closed windows etc. Is there a way of getting back my most recent session or is it lost forever?