PROBLEM: Can't login from LP on MyMedicare.gov even though it's setup properly to do so.
ENVIRONMENT: Windows 7, Firefox 65.0.2 64bit
SOLUTION: Turn off "automatic login" under "Advanced Settings". Manually click on "Signon" button after username and password are filled in. Wait a few seconds... you are in!
BACKGROUND: With automatic login turned on, the web site automatically goes to a Registration page not allowing access to a link that let's you troubleshoot user name or passwords. Turns out, your username and password are probably just fine. But, when "automatic login" is turned off, and manually executing "signon", everything works out fine. Wasted an hour or more with their tech support, trying to reset password, locking account out... you get the idea.