Additional Information I didn't configure 'Secondary Email', 'Recovery key' and 'Two-step authentication'.

You probably can't as you need access to the Firefox account and without access to that email account it isn't possible to reset the password to regain access. Is that the only device connected to this account as Sync is meant to sync data between other devices? *https://support.mozilla.org/en-US/kb/ive-lost-my-firefox-sync-account-information *https://support.mozilla.org/en-US/kb/reset-your-firefox-account-password-recovery-keys If you can expect that you lose access to your primary email address then you should have setup a secondary email address and confirm this address before losing access to the primary email address.