I forgot I had this installed and it just saved my butt. For whatever reason, a Firefox window would not open after closing and restarting my PC. Tried a lot of things to get them back but then remembered this add on. Needless to say, I got my lost window back.

Great addon! I love it! But, since a few weeks I got always this message, when I open the browser:

Simple Tab Groups addon conflicts with the following enabled extensions:

Enabled:
Tab Session Manager

To avoid losing tabs or their location in windows and groups, it is strongly recommended to turn off or remove enabled extensions that conflict with the Simple Tab Groups addon. You can do this on the addons settings page "about:addons" or by pressing the key combination Ctrl+Shift+A

???

This extension saved my butt! I had to reboot my computer (forced to do so by Microsoft Windows update actually)... and when I opened Firefox, it didn't restore my tabs for some reason. This extension restored the previous session perfectly.

Love it, much better than many other clumsy "session sync/save" extensions. Unintrusive, lightweight... I'm proud of you sienori