Rated 5 out of 5 stars

Session Manager by M. Krfat is the best extension available to manage sessions. It took me a while to fully grasp its potential but with time it has become an essential part of my browsing experience. Unfortunately it does not support (yet?) the latest Firefox Quantum update (Nov 2017). Hopefully it will. Anyway thumbs up for the great work! Update: just wrote him to flag the issue.

This review is for a previous version of the add-on (0.8.1.13).