I'm sorry to hear that. Just so you know. Tab history can be deleted if the addon is removed. Yes there were some reported cases where it went blank even without that, but in the case of Bookmarks. If any bookmarks was removed after firefox crashed, that can be the addon fault. The addon will never under any circumstance delete Bookmarks randomly. It will only delete if you specifically delete something yourself but other than that, what is saved as bookmarks (the Session tab) remains saved and will never be deleted by the addon even if you remove the addon. Bookmarks are there and it was the only way to make sure that data will be preserved no matter what happened to the addon or if you removed it. I can assure you that if you lost any bookmarks Firefox the addon is not the one to blame here. Make sure you backup your bookmarks once is a while, or use a Firefox account to sync then across many devices. Usually Firefox keeps multiple bookmarks restore points, just make sure you check all of them because I really don't know why would the bookmark vanish just like that. If you need more details please contact me over email (use the Feedback button from the addon)