The external program may have loaded a different installation or profile. Visit about:profiles in the address bar to see available profiles.

Yes I know that the external program launched firefox. The problem is that on the launch, firefox now doesnt provide me the option to restore previous session. So all the tabs in the multiple windows, isnt restorable. Some of the tabs and windows I had been keeping open for a year and would reference as needed. How can I restore previous session to retrieve a year of research with out having to search and individually open windows via history.

Note that on Mac closing Firefox can be more complicated because you can close all open windows, but keep Firefox running with the menu bar visible or minimized in the Doc.

Make sure to use "Quit Firefox" with all windows still open, especially if you want to use "Restore Previous Session". Otherwise check "History -> Restore Previous Session" and "History -> Recently Closed Tabs/Windows".