Common Vulnerabilities and Exposures assigned an identifier CVE-2005-2395 to the following vulnerability:
Mozilla Firefox 1.0.4 and 1.0.5 does not choose the challenge with the strongest authentication scheme available as required by RFC2617, which might cause credentials to be sent in plaintext even if an encrypted channel is available.
Upstream bug comments suggests that Mozilla does not plan to address this issue in the short term. This seems to affects the version of Firefox shipped with Red Hat Enterprise Linux 5 and 6, and also Fedora.
Closing this bug as WONTFIX currently.