Sidebery - Manage your tabs and bookmarks in sidebar.
Firefox Multi-account Containers - Sign in to two different accounts on the same site
Tree Style Tab - Tree Style Tab is an all-in-one Firefox extension that provides ability in order to operate tabs as a tree.
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.
Multilogin - Connect to websites as a multitude of different users
Tab Workspaces - Organize your tabs into workspaces.