HELP! Is there any way to restore a session in Firefox if it is greyed out?

i was using firefox with over 30 tabs open, went to go operate another application and when i went back to firefox all the tabs were gone, the application never quit but the tabs were gone

i went to "history > restore session " but it was greyed out

i then went to about:sessionrestore in the url and it was empty

i read a long time ago that theres another way to retrieve your tabs?