I had a previous session of 4 open windows each with their own selection of tabs. I had exited Firefox the correct way, so that when I opened it again next time, all I would have to do is click the "restore session" button at the bottom of the main page that opens.

My sister used my computer without my permission, opened Firefox, and proceeded to open a whole bunch of tabs of her own - and did not click restore session. How do I get that session back? Now when I click "restore session" it just gives me her session! I want the session before that... please tell me there is a way to get that second last session back???