Check out this links

• https://support.mozilla.org/en-US/kb/how-do-i-restore-my-tabs-last-time
• http://kb.mozillazine.org/sessionstore.js

• Session Manager: https://addons.mozilla.org/firefox/addon/session-manager/

As far as I can tell, this does not answer the question. This is a problem with tab groups - if you mistakenly close tab groups, you can only recover the last 10 tabs.

I had a window with many more than 10 tabs which I reopened each session by going to History > Recently Closed Windows. I knew this was risky - I could lose this if I did not keep it in an open window or recently closed window. So I was looking for a way to save this window with all the tabs. I looked into tab groups and, not knowing what I was doing, I closed the groups of tabs. No recovery for other than the last 10 tabs. And open tabs are not necessarily in recent history unless you have accessed the tab and refreshed.