hello NissiBloem, firefox sync is not designed as a backup service but to keep multiple devices on the same level.

in order to access the data in your sync account you'd need three components: the username, the password & the recovery key generated during the original setup of the account (you're prompted to print it/save it/write it down while setting it up). in case you have all those three pieces of information available, you can go to firefox > options > sync > set-up sync > i have an account > i don't have the device with me in order to link firefox to your account.

O,ok. I thought and understood it as a backup service also. I wouldn't be surprised if I am not alone in this assumption. Can't firefox rebrand it or something to get the confusion out of the way?!? It should be at least very helpful if it was a backup service also!! Now al my bookmarks is gone!!!