hello, firefox sync 1.5 and the palemoon 1.1 implementation of sync are not compatible.

hi philipp, can you tell me how to use a recovery key then, either in firefox or palemoon browser?

i don't understand your question: does your recovery key belong to palemoon sync or firefox sync?

The recovery key is no longer part of Sync 1.5. It was replaced by a hidden implementation of a new 'key' setup that isn't user facing.

PaleMoon uses the old 1.1 version of Sync which isn't compatible with Sync 1.5 . https://www.palemoon.org/sync/

PaleMoon has its' own support forum over here: http://forum.palemoon.org/index.php