The best currently for Quantum.

Thank You So Much Dear "Sienori" , For This Brilliant addon , Excellent addon

excellent, the best session manager at the moment. if i may, i'd like to point out a little problem regarding favicons and (i think) "auto tab discard" extension: when TSM saves a session with some "discarded tabs" by that extension, the modified favicon disappear when reopening the session.

This is a must-have, life-saving add-on! Ever since TabMix Plus stopped working, I was looking for an add-on that would ensure that my tabs are restored when Firefox has a bad crash and can't restore itself.
But this add-on does so much more. It allows you to store your session manually or automatically. So whenever you notice that you are missing a tab (web page) from a few weeks ago, chances are good that you can find a backup.

Phenomenal!! Essential for my productivity. Cannot recommend highly enough

Does Tab Session Manager supports Simple Tab Groups? What should I do if FF suddenly crashes? Will Tab Session Manager restore all my tabs AND GROUPS?

this is a great little add-on. so many times, while drunk i have closed windows to come in the next morning to wonder where they went. Thanks

Tab Mix Plusのセッションファイルをインポートするのは可能でしょうか？前からはそっちを使っていましたがつい最近動作がおかしくなりこちらに移行するのを決めましたけど、今Tab Mix Plusではなぜか保存してるタブの1割程度しか復元できない状態ですから、もし変換が可能ならぜひ試してみたいです。
ちなみにブラウザはWaterfox使っています。
不慣れな日本語ですみません。

It saved my life a few times already. A few months ago firefox started crashing and losing all tabs on linux, and after I installed this addon I had a few crashes that I survived and had a way to restore all my tabs. A real life saver.

「素晴らしい、感謝しきれない。」
ただ以下のバックアップの読み込み方法は不明。
--
バックアップを保存する
ブラウザの起動時にセッションのバックアップファイルを作成し，ダウンロードフォルダに保存します。

As one of the early adopters, I have been using this add-on from the time Quantum disabled "Sessions Manager". Over a year, this add-on has come close to the functionality of the "sessions manager" add-on by Michael Kraft. I must commend the dev, sienori on his relentless efforts through regular updates in helping the Firefox community. Kudos to the work! The only grouse I have though is that sometimes, I get the IndexDB erroe which surprisingly, automatically resolves itself in a few days. Can't blame for it. Have a good one dev! Cheers.