Something ive wanted for long time... Rated 4 out of 5 stars

Works extremely well. Only wish i could rearrange the groups etc.

As to how well this behaves with other extensions. TabMixPlus sessions didnt work well, but using Session Manager instead works nicely. Also TMP multiple rows does not work but theres a workaround using custom Stylish "style".

Make sure you follow the TabBar option change (Scrollable without buttons) as instructed in the style page.

http://userstyles.org/styles/10989

This review is for a previous version of the add-on (2009.01.04.01branch1). 

Thank you for the invaluable suggestion.

Thank you for the invaluable suggestion.
It was confirmed that the multi-rows tab was possible by this Style Sheet.
And, I confirmed that it can apply this Style Sheet by TabGroupsManager without "Stylish".
It is an almost ideal method because it can correspond neatly even if the Group is switched.
The only problem is that the width of the tab is always minimized.
When the Multi-row tab of "Tab Mix Plus" cannot be used well, I will achieve it by this method.
However, even if this method will be used, it takes time for a while.

The next version can rearrange of the Group by Drag & Drop.
In addition, even if Firefox is ended, the order of the Group can be preserved.

It is difficult to deal with the session manager of "Tab Mix Plus" because SessionStore of Firefox is used more in the next version.