I would give this extension 1 star, but I can't. Because this is the only one extension, which works for saving and restoring sessions for Firefox. There is no alternative.
I can't give 5 stars however, because extension is very buggy and looks like not even tested by developer properly.

Obvious issues are:
1) If you move tabs between windows - then session tracking gets screwed up Tab Session Manager cannot save this session anymore. Nothing helps. I tried disable/enable back extension. I tried remove extension from Firefox and re-install it back. Nothing helps. Moving tabs between windows is Firefox core functionality. Also its possible to move tabs between private windows. This makes it impossible to organize tabs across multiple windows when using Tab Session Manager.
2) Tab Session Manager export-import extension settings - doesn't work properly. After you import settings you notice that many options are not respected by export and do not restore back. A lot to list them all, but for sure I remember: theme, auto-save intervals, backup and other options.
3) Keyboard shortcuts for saving sessions - do not work at all. No matter which key combination, I tried everything. Only one shortcut works - open extension menu drop down.
4) Bug in intervals. If you set interval to 60 minutes - nothing gets saved every hour. I had to set to 50 minutes because of this.
5) If tracking is screwed up because any unknown reason - then it's impossible to reload extension and re-capture current session and it will always fail to save current session.

But what really works great is regular popup that asks about donations.
I would happily donate, but currently I am not aware if developer cares at all about above mentioned issues, whether those will get fixed.