Change all instance of user.js located under the script directory as well as the instance located in %appdata%\Hewlett-Packard\LoadRunner\Web2\LrWeb2MasterProfile
Modify the following entries or add it in case it does not exist:
user_pref("network.automatic-ntlm-auth.allow-proxies", true);
user_pref("network.negotiate-auth.allow-proxies", true);
user_pref("network.negotiate-auth.trusted-uris", "https://<your_domain_name>");
user_pref("network.automatic-ntlm-auth.trusted-uris", "https://<your_domain_name>");
