As I sat beside my fancy library online (*cough* bunch of Firefox tabs *cough*), to my horror, all but the last bookshelf had vanished! All those HOURS curating the finest text that would tickle my brain... lost! Thanks Mozilla devs, for the timely updates.
I was gutted. As I fumbled through solutions online on restoring my sessions, I couldn't find one that would bring back the tabs grouped the exact way this add-on had done. Then, I happened to be in my downloads folder. And there it sat, with a smug on it's face, the elusive BACKUP FOLDER from this wonderful Manager by ''sienori'' Awesome (I am sure that's your last name).
In the rare few moments of productivity in the past, where I was playing with the settings, I had switched on the sessions backup option (DO IT!). After that it's just a simple click to import the session.
Thanks dude/tte!