What are some alternatives?
When comparing Tree Tabs and Tab Utilities, you can also consider the following products
Simple Tab Groups - Create, modify and quick change tab groups. Features:
Tabs Outliner - Next Generation Session, Windows, Tabs Manager and a TooManyTabs Solution That Really Works.
Simplified Tab Groups - This Firefox addon provides tab grouping features similar to the removed TabView/TabGroups/Panorama...
Tree Style Tab - Tree Style Tab is an all-in-one Firefox extension that provides ability in order to operate tabs as a tree.
Conex - TabGroups married with Tab Containers and bookmark & history search
Session Box - Using websites with multiple accounts at the same time is made easy.