Since http://code.google.com/p/chromium/issues/detail?id=7338 and https://bugzilla.mozilla.org/show_bug.cgi?id=479880 there was no clean way for a proxy or captive portal to get a web client to display an authentication dialog when user credentials expire while he is browsing on an https url. The IETF finally set up to fix this problem and defined a standard HTTP error that lets access control equipments tell the web client authentication or re-authentication is needed and where the authentication form is located. http://tools.ietf.org/id/draft-nottingham-http-new-status-04.txt → <http://www.rfc-editor.org/queue2.html#draft-nottingham-http-new-status> (the spec is approved and in the queue for publication as RFC) Please add error 511 handling in Fedora Firefox, so Fedora desktops can be used on corporate networks that implement HTTP error 511 as proxy authentication method
Thanks for report and escalation to upstream too, we're going to track this issue on Mozilla mozbz#728658.