Doesn't work at all. Don't waste your time. This extension should be removed from mozilla store, because it doesn't work and 4 years not updated.

This only worked the way it says it should once or twice. I have a research job that had 56 tabs open in about 6 windows. Even though I have FF restore my tabs and windows, I have this extension as a safety net. So when that whole session did not come back, I used this extension to get a similar saved session. FF went bonkers. The "restored" saved session opened a new tab, then duplicated itself and the new tab action about 25 times. Restarting had no effect. It's just broken and buggy. You should not rely on this to save your work! I now have to dig through hundreds of entries in my history to get that work back.