Greetings! It appears that Firefox has sent a verification mess to either your phone or email. Please check those for a message form Firefox. In your email, be sure to check your spam mail as well.

This is called 2FA (Two-Factor Authentication). When you asked the site to send you the code, it should have opened a webpage where you can enter the code they sent. Note: the code is only good for a short time. You may have to start over again.