Tab outliner is, imo, even better than FF's TST because outliner can also work as a persistent session/bookmark manager. It is really important to someone like me who doesn't like seeing a hundred tabs and yet want to keep them in tree. Outliner gives you the ability to close a tab without removing it from the tree so you can re-open it later. Some people use bookmarks for it, but to me this is a much more light weight and saner way of doing session management (essentially "temporary" bookmarks, if you will)

> It is really important to someone like me who doesn't like seeing a hundred tabs and yet want to keep them in tree.

Yes! I love that I can context switch by opening and closing entire windows of (a manageable amount of) tabs.