Mozilla is divided into several separate support/service areas. Each uses their own username and password logins. Open the Password Manager. One of the first entries should be the sync login data. It might have a blank entry for '''User Name.''' Type '''about:preferences#security'''<enter> in the address bar. Look under '''Logins, ''' Note: For Firefox v56+ its; '''about:preferences#privacy''' Look under '''Forms & Passwords ''' Or type '''about:logins'''<enter> in the address box. +++++++++++++++++++++++++++++++ Turn on '''Remember Logins. ''' To check the passwords you have listed, press '''Saved Logins. ''' Press the '''Exceptions''' button and see what's inside.