Thank you for review. That exact feature was available prior to the WebExtensions version. As much as I wanted to do something about it was simply not possible because Firefox just killed the previous API that I was using to track pinned tabs. But, I think that I might be able to find a hack to do this again (I have several ideas that might work - just figured them right know) and I'll try to make it available into the next update.

Regarding the button. Yes, if the feature is implemented it will be there. The previous version actually had one there but I had to remove it because it was no longer working, but like I said ... I'll solve that with the next update.

Regarding the restore order. I will look into it and make sure they are restored as they should.

Hope that once these feature are implemented you will consider rating it 5 stars.

Glad that you like the addon and also, thank you for the great rating.
Regarding the ability to export and import saved sessions, theoretically it's possible and I might add it in the feature but because the WebExtensions is still limited and I can't truly import bookmarks with it may create lots of problems for anyone using Firefox Sync.
That being said, somehow you can still export all your bookmarks right now and those do contain the saved sessions but also all your other bookmarks. I'll see what I can do regarding this feature. I might find some solution after all, maybe by using the Bookmarks Import feature and not something through the addon API it might work.

For the update (2019/08)

Sorry for the issue with History. There was a bug in the previous version (that only happened in some specific conditions where everything in the history would be deleted) and somehow it seems that some users continue to have that. There's seems to be an strange incompatibility that somehow I can't replicate myself to find out the bug. I'm pretty sure that if you reinstall the addon everything will be working flawlessly again and probably you won't have any more problems. Everything you saved as bookmarks is safe so you can uninstall and install it without any issue (by doing that you only lost History but since it's already blank it is not a problem.)

I just noticed this update by chance because I observed that one 5 star rating disappeared. Sadly the review section is really stupid and nobody is ever notified of an update so please it you ever have other problem it's better to send me a mail through the feedback button. I guarantee you that there's a great chance to solve everything by discussing than just updating the review (of course you can do that as well but it doesn't really fix anything and that's not really helping anyone, bugs can remain in the app and you don't really fix the issue)

------------------------------
Thanks for the review. If I'm not wrong and you just changed the rating from 4 stars to 5 stars, I really appreciate that. It's really hard to try to meet everyone's expectation but I hope that in time by adding new features things will only get better.
I might be able to add a form of syncing for the auto-saved history sessions in the feature, but that only if the API is able to understand different devices (at this moment I can't figure out a solution for this) because otherwise one device will overwrite the others and that would clearly not be something desirable.
For bookmarks sync service - Firefox account is the best option.

Thank you for the nice words and the positive review. Now... I only need to make sure it remains the best one :), with many improvements and features.