After a year or so of not using this extension, I was very pleasantly surprised when I installed it again today. It seems a lot more stable than what I was used to.
As a Tree Style Tab user, I highly recommend this extension.

Edit: The latest update has a much clearer layout which can be opened in a separate tab. Very useful.

How to export sessions outside Firefox? Thanks!

Thanks for pointing out the Firefox bug that prevents add-ons from running by incorrectly flagging them. I love the Tab Session Manager. I rock 4 windows with ~20 tabs on each at any given time. Thanks a mill!

What I wrote previously (ignore):
"Please get your add-on signed, it has been removed from Firefox's list of approved add-ons and thereby inactivated on my computer. I'd give 5 stars otherwise."

Пожалуй самое удобное и хорошо зарекомендовавшее себя расширение, пользуюсь больше года и не подводило до недавнего времени, когда количество вкладок перевалило за 400!! Теперь программа не открывает окно с выбором сохранений, сбрасывал настройки, удалял и ставил по новой.. не работает ((

From now Firefox works only with signed add-ons.
Please sign your add-on.

PS temporary solution from Firefox docs
about:config xpinstall.signatures.required = false

Works great but does NOT Support Multi-Account Container. Every time session is restored, you'll have to reopen the tabs in the desired Container which is really annoying. Otherwise, it's a great must-have add-on.