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."

firefox自体のセッションストアが飛んだのでプロファイルを初期化してこのアドオンから復旧しようとしたのですが、2019/3/25以降にバックアップされたセッションをインポートしようとすると読み込みには成功するもののセッションリストが「全て[0]」のままです。
なお、その間タブの数は1500～1600ほどで大きくは変わらないのですが、3/12に56MBだったバックアップファイルがどんどん肥大化、読み込める一番新しいもので258MB、今月には503MBになりました。

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

It worked really well until the fateful day where all my sessions went missing, and I can't even use it anymore. I can't export my sessions either.

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.