Two-Factor authentication (2FA) works with a 6-digit time-based code (TOTP:Time-based One-Time Password) that is valid only for thirty seconds, so make sure that time and timezone are correct on all devices especially on the mobile device with the Authenticator App that generates the TOTP code. More info:

• https://support.mozilla.org/en-US/kb/secure-firefox-account-two-step-authentication
• https://support.mozilla.org/en-US/kb/what-if-im-locked-out-two-step-authentication

There are extensions for Firefox that you can try and compare the TOTP code they generate with the code from Google authenticator.

• https://addons.mozilla.org/firefox/search/?type=extension&q=authenticator
• Authenticator https://addons.mozilla.org/firefox/addon/auth-helper/

I have an idea wat it OTP. It's not my side error. I tried 10 12 times. Same thing happened. Authenticator apps not new to me. I use these everyday