This happens when the confirmation email that Firefox sends returns an error message. This usually means that the email did not go through due to some issue with your email provider or that your email provider blocks messages from Firefox. Sometimes, automatic vacation replies or other instant replies that you have setup on your email address can cause this to happen. To make sure that the confirmation email goes through, try adding <code>accounts@firefox.com</code> to your list of trusted senders and/or your email's contacts. This should make sure that your email provider allows the message to go through. The block on your account should only last for 24 hours, after which you can try to sign into the account again. See [[I'm having problems confirming my Firefox Account]] for more information. Hope this helps.