The bug may be deeper than just the password retry. Completely closing all Firefox sessions and returning to the P2P signin page, When attempting to use Yahoo ID to sign in, I was presented with a Yahoo sign in page (which apparently worked for Yahoo -- I can access my email through FF now) but still get "Unknown User" for Yahoo P2P signin.
The bug may be deeper than just the password retry. Completely closing all Firefox sessions and returning to the P2P signin page, When attempting to use Yahoo ID to sign in, I was presented with a Yahoo sign in page (which apparently worked for Yahoo -- I can access my email through FF now) but still get "Unknown User" for Yahoo P2P signin.