The Recovery key can be used if you forgot the password of the Sync account and need to reset this password to regain access to the account.
Normally you would lose data stored on the Sync server if you reset the password, but if instead you use the Recovery key then you can keep access to this data on the Sync server.
The recovery key is a 32-character key that you need to generate beforehand (i.e. when you create the account) and you would have to store this key in a safe place and be able to access and use it when necessary.
Of course you can do the same with the actual password to prevent forgetting the password.
The Recovery key can be used if you forgot the password of the Sync account and need to reset this password to regain access to the account.
Normally you would lose data stored on the Sync server if you reset the password, but if instead you use the Recovery key then you can keep access to this data on the Sync server.
The recovery key is a 32-character key that you need to generate beforehand (i.e. when you create the account) and you would have to store this key in a safe place and be able to access and use it when necessary.
Of course you can do the same with the actual password to prevent forgetting the password.
*https://support.mozilla.org/en-US/kb/reset-your-firefox-account-password-recovery-keys
