Firefox asks for user name and password on internal sites: http://perfect-blog-url.blogspot.hu/2013/07/firefox-asks-for-user-name-and-password.html

Enabling NTLM Authentication (Single Sign-On) in Firefox: https://www.liquidstate.net/enabling-ntlm-authentication-single-sign-on-in-firefox/

Firefox add-on for easier management of NTLM pass-through authentication : https://github.com/tillig/FirefoxNtlmAuth