How do I save sessions (permanently) or sort of favorite them so that I can open the groups of tabs later on? Can we replicate Simple Tab Groups functionality with Tab Session Manager ? Thanks.

Very good addon!
Does only save the active page for each tab. Having an option to save each tab history will be great, but it seems that it is due to a limitation of Firefox's API.

Good session manager, has good features. Sessions open fast. A problem for me after saving a fair number of sessions was slow opening time. I'd start FF and the TSM would not populate with sessions for perhaps 10-15 minutes. Is it loading sessions all that time? Perhaps should load auto-save sessions last? As said in another review, wording of how to save backups is confusing. Better wording: "Save location must be under the Download Folder (set in browser settings)."

One of the most useful add-ons.

very useful tool for all MFF Users like me..

The original order of the tabs is lost when the window is restored.
In my case, the extension is to blame: [https://addons.mozilla.org/en-US/firefox/addon/tab_position_options]
The error is in option: [New Tab][Right of current tab],
It works if you leave it as [Default].

Another solution is to use
https://addons.mozilla.org/en-US/firefox/addon/tab_position_options

with the other extension

https://addons.mozilla.org/pt-BR/firefox/addon/always-right

最新版6.8.3だと、セッションを開きなおした時に保存した順番とは異なる順に展開されます。
保存時点でアクティブなウインドウのアクティブなタブだけ先（右）になるっぽい
具体的には一旦複数のタブを開いてセッションを保存、ブラウザ落としてセッション開いていくつかアクティブにしてもう一度保存、再度セッションを閉じて開き直すと再現できるはずです
12345の5タブ保存してあるとして1（今見ている）23（アクティブ）45（保存したのを開いたまま）でセッション保存して、ブラウザ落として開き直すと1（アクティブ）4523 として開かれます