What are some alternatives?
When comparing UndoClose and Tab Utilities, you can also consider the following products
Tree Style Tab - Tree Style Tab is an all-in-one Firefox extension that provides ability in order to operate tabs as a tree.
Tabs Outliner - Next Generation Session, Windows, Tabs Manager and a TooManyTabs Solution That Really Works.
Undo Close Tab - Reopens the last closed tab.
Session Box - Using websites with multiple accounts at the same time is made easy.
MySessions - MySessions is a simple session manager.
Tab Tally - Firefox add-on, displays how many tabs are open.