Is there a way to select an older session to restore, or does Firefox only keep the most recent one on file?

Here's the situation: Firefox was slow to restart after a hang, so I restarted my computer. On restart, Firefox did not restore the previous session, and the session-restore setting was switched off in Options. I re-selected it, and tried re-starting Firefox in the hopes that the session I originally wanted restored would come up, but of course I got the most recent session instead.