Tab Groups
This add-on will not receive any more updates!
It will cease working by next November with Firefox 57. Click here for more info. Feel free to fork and use however you like.
AMO url: https://addons.mozilla.org/firefox/addon/tab-groups-panorama/
Babelzilla page: https://www.babelzilla.org/index.php?option=com_wts&Itemid=0&type=show&extension=5749