The addon will let you create sessions with titles and restore them to the current tab or a new window. It does this pretty well.
I tried this out as an alternative to "session manager" which is no longer support in FF 57+. Unfortunately this extension does not have an import feature for "session manager", or have folders to group sessions.
The UI and usability could do with some refinement as well.

In reply to developer: How can you import from session manager if it does not support folders for sessions? Does it dump them all into 1 list?