When does FoxyProxy use my PAC file?
When you configure a proxy in FoxyProxy and select “Automatic proxy configuration URL” on the “Proxy Details” page, you’re specifying that FoxyProxy use a PAC for any patterns associated with this proxy configuration. In other words, for each URL that matches a URL pattern defined by a proxy configuration specified to use a PAC, FoxyProxy calls that PAC’s FindProxyForURL() implementation. The return value of FindProxyForURL() determines which proxy (if any) is used.