Tree Style Tab - Tree Style Tab is an all-in-one Firefox extension that provides ability in order to operate tabs as a tree.
Firefox Multi-account Containers - Sign in to two different accounts on the same site
Simple Tab Groups - Create, modify and quick change tab groups. Features:
Lightbeam for Firefox - Mozilla is the not-for-profit behind the lightning fast Firefox browser. We put people over profit to give everyone more power online.
Sidebery - Manage your tabs and bookmarks in sidebar.
Multilogin - Connect to websites as a multitude of different users