This add-on has potential with some more development.
Cons: Very difficult to move tab from one group to another. Would have though you could have moved tab around in edit, but cannot see how you can. Slows Firefox when loading a group that you have many tabs in group. It seems to load each one before response is back to normal. No Drag and Drop. Does not show the favicon in edit or quick list view. Open a new window and pinned tabs are not included.
Pros: Nice edit layout. Works with 57.x