Firefox Proxy Preferences
You can proxy HTTP and HTTPS traffic from Firefox by either configuring the global proxy preferences or by following these steps.
Note the port number - Proxy.app listens on a designated port number (by default port
8080). To get the current port number simply open the Preferences from the application menu (key equivalent
Setup the Firefox network preferences - Go into Firefox Preferences > Advanced > Network > Settings. Select manual proxy configuration. Inside the HTTP Proxy and SSL Proxy fields type
localhost. Port numbers should be set to the port number value obtained from the previous step. Press OK button apply the change.