Proxy Authorization Required

First off all, change the network settings from manual to automatic and leave the Firefox proxy setting set to manual.

For the terminal to work with your proxy, do the following: Create the following file : /etc/apt/apt.conf, open the terminal and type:

sudo gedit /etc/apt/apt.conf

Edit this file according to your proxy details:

Acquire::http::proxy "http://username:password@yourproxyaddress:proxyport";
Acquire::https::proxy "https://username:password@yourproxyaddress:proxyport";

If your proxy doesn’t require a username, then those statements take the following form: Acquire::http::proxy yourproxyaddress:proxyport";

To be able to add a PPA, you will need to export your proxy settings open the terminal and type:

export https_proxy="https://username:password@yourproxyaddress:proxyport";

export http_proxy="http://username:password@yourproxyaddress:proxyport";

Once you have done this, to export you will need to add a -E after sudo, e.g. sudo -E apt-get install python-software-properties