Probably the best FF addon ever. And showstopper for me, because it does not work on v57+. But this is Mozilla's fault and not author's.
So, no FF 57 for me, I will stay on FF ESR release as long as it goes, then move so so other browser, preferably WaterFox if TabGroups will work on it.
Shame on you, Mozilla. In v57, there is simply not functionality or extension for managing large group tabs. Damn you!