Ubuntu – Setting system wide proxy through bash script (Temporarily)

Firefox just can't do the standard thing and use environment variables (though to be honest this is partly justified as the standard thing doesn't allow for proxy autoconfiguration files). The preferences for static proxies are

user_pref("network.proxy.http", "wwwproxy.example.com");
user_pref("network.proxy.http_port", 3128);
user_pref("network.proxy.type", 1);

There's a Firefox extension to use $http_proxy and similar environment variables: Environment Proxy.

Recent versions of Firefox supposedly use the usual environment variables by default, or if the proxy type preference is explicitly set to 5 (“Use system proxy settings”), but it doesn't work for me with the version in Ubuntu 10.04.

user_pref("network.proxy.type", 5);

System wide proxy settings are just another consolidated place for proxy settings. It actually modifies the places where different apps' config files. Have you noticed, system wide proxy setting asks for password 2 times? This is mainly because of the modification of two admin files which corresponds to config file.

And yes, from 10.10 and 11.10, some apps have been left out of system wide proxy setting most notable among them is the synaptic.

and moreover, apps can bypass the system wide setting and make use of their own setting again most notable synaptics and Mozilla Firefox(which contains system settings option as well).