FIXED: Unfortunately, the latest version (4.4.2.1, from 26 Feb 2020) contains 2 major bugs, which ruined the previously awesome add-on:

1) When I now click the STG icon in the Firefox (v73.0.1) toolbar, the add-on shows me a listing of the _tabs_ in the active group, rather than a listing of all the _groups_ that I have created.

2) The "Move tab to group" functionality (from right-click context menu) no longer works. It seems to do absolutely nothing now.

(Assuming that the above bugs will be fixed soon, I'll gladly recommend the add-on to all users!)

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EDIT (5 March 2020): Yes, the update to v4.4.2.5 indeed fixed the bugs mentioned above. Superb! Thank you Drive4ik. =) =) =)

Дополню сообщение gamover
Версия 4.4.2.4, последнее обновление 26.02.2019, новые обновления не находятся. Кнопка TabGroup все еще показывает по умолчанию не список групп, а список вкладок в группе. Раньше было наоборот

Last update changed it to show all the tabs in your current group rather than the groups, making it extremely tedious to switch between groups. The addon is much less useful now. Edit: Fixed

If you use a lot of tabs and like to keep your sessions organized around themes, this is an essential tool. Don't leave home without it!

upd: Now that I understood, how to use regular expressions with this extension, it's become really helpful. Thanks for your help.

Hi. Love this! Took me a while to replace tab groups but finally I found this! Great job. I'm loving the workflow improvements it brings and it's first class in reliability too. Thanks you for creating this for everyone crying about the loss of tab groups, this is actually better!

DEV: One thing i'm not certain about is if it's possible to include pinned tabs under tab groups i create, is this possible?

This addon saves my ass. An incredible addon.

Has minor issues, but it's great. Went essential in seconds. Thanks, keep up the good work!

I just love, love, love the ability to put all my different research/interests/archive into groups.

It's awesome ! Really helps to manage >100tabs. Thank you so much!