Cache Access Denied.

Since autoupdate FF from version 19 to 20 I can't acces any sites through our squid http proxy over domain authentication. Problem is the same on 2 PCs, one with Windows XP, and one with Windows 7. IE and older FF versions works fine. Problem is NOT related to foxy proxy - I've already tried without any add-ons. With https connections, FF just informs thath proxy server refuse connection. With http squid error page is displayed: ERROR Cache Access Denied. The following error was encountered while trying to retrieve the URL: http://www.mozilla.org/ Cache Access Denied. Sorry, you are not currently allowed to request http://www.mozilla.org/ from this cache until you have authenticated yourself. Please contact the cache administrator if you have difficulties authenticating yourself or change your default password. Generated Tue, 09 Apr 2013 19:19:13 GMT by proxy (squid/3.1.6)