Network proxy can be configured in browser Settings for Charles proxy. This includes browser FireFox, Chrome, Safari, IE. And the way for the configuration are similar across Windows and MAC. Just simple set up a proxy in FireFox or Chrome Settings and let it point to local IP of machine with port number. Then Charles proxy can catch all traffic of browser.
Windows
How to configure a proxy in FireFox for Charles proxy in Windows
How to configure a proxy in IE for Charles proxy in Windows
MAC
How to configure a proxy in FireFox for Charles proxy in MAC
How to configure a proxy in Chrome and Safari for Charles proxy in MAC
One thing needs to mention, after configure a proxy in browser, don't forgot to take them off if you turn Charles off. Otherwise, Internet will stop work because browsers tries to send traffic via a proxy that you set up in browser but you have closed Charles.
How to configure a proxy in FireFox for Charles proxy in Windows
How to configure a proxy in IE for Charles proxy in Windows
How to configure a proxy in FireFox for Charles proxy in MAC
How to configure a proxy in Chrome and Safari for Charles proxy in MAC
* But just be careful on Mac, once this configuration made on Mac in System Preference via Chrome, it also changes the proxy settings of Mac machine with proxy. It means your machine will proxy all Internet traffic in and out. Then when you turn Charles proxy off, then Internet will be closed as well. So when you don't use Charles for proxy, don't forget to change proxy setting back in System Preference. This is different from when you enable MAC Proxy in Charles proxy. When you enable MAC Proxy in Charles proxy, turning off Charles proxy will disable proxy function of Mac machine. But if you made change in System, turning off Charles proxy, it won't disable proxy function.
