I created a secondary email in my Firefox account and then generated a recovery key. Then I decided to use a different email as my secondary. After that I tried to update the recovery key (assuming the first key is linked to the first submitted secondary email) but FF said there was already a recovery key established. So, if I ever need to enact the recovery key, will firefox accept the initial key from the latter secondary email?
I think that the recovery key is linked to the password of the Sync account and not affected by an email change. You can possibly test this by changing the password and see whether that allows to generate a new recovery key or that you are prompted to do this.