There is a bug in this add-on which I thought would be resolved by now. I am on Firefox Quantum and 'Restore all tabs' does not work. It just loses it. I have spent countless hours going through my history to visit the pages again. Restore all fails every single time. Luckily, I found a way to stop this. I lock the tabs nowadays and share it as a webpage to use them. Very inconvenient. Please look into this issue