User Agent: Mozilla/5.0 (Windows NT 6.1; rv:48.0) Gecko/20100101 Firefox/48.0 Build ID: 20160726073904 Steps to reproduce: (in this network we can access the internet through a web proxy with authentication) control+shift+p open any site (google.com) Actual results: firefox asks for proxy password Expected results: firefox should use stored proxy info, as it does in non-privacy mode

Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:48.0) Gecko/20100101 Firefox/48.0 Could you please give us more details regarding the configuration you've made under the "Connection Settings" in Firefox? Also have you enable the radio button for "Do not prompt for authentication if password is saved"? Checking this option might solve the issue, the dialog for authentication won't appear if password is saved.

I use manual proxy configuration, hostname and port specified, "use http for all" checkbox selected. "Do not prompt for authentication if password is saved" was off (strange, firefox never asks me for proxy pass). Turned on, but doesn't seem to do anything: opening privacy mode and connecting to any site pops up "the proxy mod-proxy://$host:$port is requesting username and password". Pressing cancel leads to "The proxy server is refusing connections"

I can also see this on Windows XP, FF 48-49. The proxy seems to normally authenticate via NTLM (seen in HTTP headers in Web console) so I give no password. But immediately after opening a Private window, any webpage access in it causes the request for proxy password as the reporter says. Thus, private browsing does not work (I have no password).

I am assigning a component to this issue in order to involve the development team and get an opinion on this.