Safari

Open a Safari browser and click the apple icon on the top left corner. Select the System Preferences... option.

SystemPreferences
Network

Click Network

Network Advanced

On the left, select the desired network and the click the Advanced option (bottom right).

PAC Settings

Click the Proxies option in the upper bar, then, on the left-hand side, mark the Automatic Proxy Configuration checkbox, and on the right-hand side, enter the PAC file location (to use the default PAC file, use the following path: <http://ProxyHostname/default.pac>).