Wow, this is brilliant and why have I not found this before. It's so simple to use and does exactly what it says.

Compared to the old Tab Groups, I really love the concise group selection pulldown UI. I can use Simple Tab Groups' visual mode to manage tabs as needed, but don't need that elaborate UI when I'm just navigating between groups.

I'm at 3.499
I think it's a fabulous bit of code - potentially really useful. Problem is that it's not being integrated with other, more essential add-ons or features.
For me, the deal killer is the lack of coordination with ONETAB, which is one of my primary ways of keeping track of my research in a simple permanent list system. With Simple Tab all nice and neat - now I run OneTab and it's like I just powered up a chain saw at a society event.
The kicker to giving Simple Tab the boot, is the fact that multiple windows know not to let OneTab bother it. Obviously a similar feature, so perhaps I will find some way of managing those windows visually? Why didn't Simple Tab Groups think of that, instead of re-inventing the bowling alley?

great features, closest to old Tab Groups FF feature, but (currently) a huge memory hog... like, HUGE.

Excellent. Develop.

I really like this addon and the hard work of the author.

Some bugs:

1. The extension sometime reports some previously closed tabs as unmanaged
2. Performance. Noticeable lag when switching groups with many tabs / opening the popup

This is helpfull and simple!

So far the best replacement for the old tabgroup plugin by far. I recently just downloaded this and trying out, but I'm really impressed. Love the memory saving settings when you got tons of tabs in different groups. Will come back if I find some bugs, problems or suggestions!

EDIT: So a couple of things I noticed:
When trying to open a group as a new window does not work, sometimes it just opens a new blank page. It would also be nice if there was an option to take an already open window with tabs and create a group from that, rather than just one tab at the time. I don't know if it's documentet somewhere if there is a way.
When clicking or hover over the Tool tips (?) does not seem to do anything.

Correct me if I'm wrong!

Believe me, This is the best tab groups manager so far.

Amazing add on, simple to use without any troubles.

best add on for tab groups replacement so far

Thank you so much! A great replacement for the old Tab Groups I agree. This means I could finally update FF on all my computers. You, good sir, are a godsend. Great work!

Almost perfect replacement for the old Tab Groups that was destroyed by Mozilla. Only lacking sidebar support, so if you use that, be aware.

Be sure to turn on automatic backup!! Today, when Firefox crashed, the group record disappeared!!

first impression:
nicely done :-)

This looks great, just started using it and it seems like a good replacement for the old Tap Groups

Really great addon! Thanks for keeping Firefox going!