Works well! An additional feature which would help with "disappearing" pinned tabs would be: opening all links from a pinned tab in a new tab (only if the domain differs from the current site)

As with everybody else, I would like to keep the restored tab order fixed, as I need to reorder around 10 tabs each time I open firefox

Does its job well. However, I second Korkythecat's request: I'd really like to have the pinned tabs in the same order as I last set them.
It seems they get scrambled on opening the browser due to the automatic "restore all pins, then delete either of the duplicates". Maybe deleting only the right-most duplicate would solve this. (Also once I had a dupe that stayed but better that than the opposite)

I was looking for an add-on that would stop me accidentally closing pinned tabs, no luck yet, but then I stumbled upon your add-on. It works in a different way but is great except for one thing, a small gripe but would it be possible to restore a pinned tab to its previous position instead of to the far right of pinned tabs.