The title says exactly what it does.
It is Basic.
You are not be able to see your saved tabs in folder, the only way you know what is in them is by the description you have given them, it is dated, with the amount of tabs saved.
It does what its title suggests.
With more usability it would be excellent.

A little too simple:

* restored windows show URLs but not titles for non-loaded tabs
* as far as I can tell, no (indirect) support for file:// and other special URLs

This version is too basic.
I do not recommend it.

I recommend instead, either of the following two Add-ons (Extensions), which can perform the same task, and have far more options.

Tab Session Manager
https://addons.mozilla.org/en-US/firefox/addon/tab-session-manager/

Session Boss
https://addons.mozilla.org/en-US/firefox/addon/session-boss