How to Test a Proxy PAC File | eHow.com
Internet Explorer
Type "file://c:/proxy.pac" into the "Address" box, replacing "c:/proxy.pac" with the full path to the PAC file on your computer.
Mozilla Firefox
Type "file:///c:/proxy.pac" into the box under "Automatic Configuration URL," replacing "c:/proxy.pac" with the full path to the PAC file on your computer.
