My registered email address doenst exist any longer

Hi Michael, if you're still signed in to your Mozilla account in Firefox, try going to Menu → your account → Manage Account. Under Secondary email, add your new Outlook address and verify it using the code sent there. Then click Make primary next to the new address. If it still requires verification through your old email, try recovering that address through the email provider. Mozilla may not be able to bypass that security check. Don't sign out of Firefox or reset your browser yet, especially if you rely on Sync for your bookmarks and passwords.

Hello,

Firstly, you cant re-register the account to change the email.

The best course of action is to create a new Mozilla account or register another device to verify in case of lockout.

If you want, you can try clicking manage account, then click disconnect or sign out, then when prompted, confirm what you want to disconnect. DO NOT choose any option that says wipe local data. After that, create a new account and link the local data to it.