I currently use a proxy server which requires authentication in the form of an email and password. Previously, I have set Firefox to 'Manual Proxy Configuration' and input my proxy settings separately to the system proxy settings. However when the firefox proxy is set to 'use the system proxy settings' with the system proxy server address specified in the form user:pass@ip firefox cannot load any webpages. Both the email and password are URL encoded to avoid a formatting conflict with the @ symbol in the email and the server specifier. This works for the system with commands such as apt-get but produces the error above in firefox. If I am to set the system proxy settings without the username and password declaration, firefox loads (presumably using the previous authentication stored) however system commands such as apt-get prompt for proxy authentication.