Disable Proxy Authorization Required

Hello Sorry for my bad english but i don't found answer for my problem on french support. I would like to disable proxy authentication popup on firefox. I have a squid proxy who works with Windows Active Directory. Firefox send automatically windows username and password to squid. If credential are good, firefox show the web page correctly. If credential are bad or on some webpage, I have many popup for proxy authentication. I woud like to disable this popup and have an error webpage like error404 i browze about:config but don't found issue thanks