I've found the add-on Panorama View a life saver: https://addons.mozilla.org/en-US/firefox/addon/panorama-view...

I don't want to save tabs, I just need them to be separated in arbitrary and temporary visual groups. Makes management so much easier when i can just switch to another group and hide the 25 tabs i had open while researching a problem.

I can't even think to work without this thing.