Very good! Some features still missing, but hopefully they will be soon added:
- resize groups in the global view (manage groups)
- allow user to choose to open the "Manage" view when clicking on the icon (as it was the case with former "Group Tabs" extension for FF<57)
- do not close tabs when change group (it seems, according to what I've read so far, that this is a limitation due to Firefox... yeah, this is improvement... but no problem, proprietary 3rd party tools like Pocket are embedded...)

Regex filters are VERY appreciated! Keep your groups clean and make sure your github tabs are always with their scrutinizer-ci friend :)

EDIT (2019-01-16) : I've FINALLY updated Firefox (had to update Fedora 26 -> 29) and I must say that it's very nice when using this (not so) new hidden tabs API. Thanks a lot for the great job !
However, I'm still waiting for free arrangement (hopefully with group resize in the "Manage" view) and the possibility to directly open the "Manage" view when clicking on the icon => then, I'll give the fifth star!