Simple Tab Groups - Create, modify and quick change tab groups. Features:
OneTab - Whenever you find yourself with too many tabs, click the OneTab icon to convert all of your tabs into a list. When you need to access the tabs again, you can either restore them individually or all at once.
Panorama View - Tab Groups with Panorama View. Lets you easily Group and manage Tabs visually, with tab hiding.
Tree Style Tab - Tree Style Tab is an all-in-one Firefox extension that provides ability in order to operate tabs as a tree.
Session Buddy - Manage Your Browser Sessions
Firefox Multi-account Containers - Sign in to two different accounts on the same site