foxyproxy THESE FORUMS ARE CLOSED. NEW FORUMS AT FORUMS.GETFOXYPROXY.ORG

 if a pac file content as below:
 

function FindProxyForURL(url, host) {
var ip = myIpAddress();
PROXY = "PROXY 127.0.0.1:8118;PROXY a.com:8118;PROXY b.com:8118;DIRECT";
return PROXY;
}

native proxy setting of firefox supports attempt chain, other browsers(include IE,safar,chrome) totally support attempt chain.
only in foxyproxy, if you using Automatic proxy configuration in proxy details panel to connect networking. it doesn't attempt second proxy while first proxy is down.

I think this function isn't implement in foxyproxy.