Proxy settings in browsers

Question

I have a couple of questions - would be happy with any tips advice for either/both of them.

1) Is there any way to set up proxy settings on browsers automatically without having to go into settings and typing the port number etc.? Ideally I would like to run a script that does this automatically.

2) Secondly, I know I can use a PAC file to automatically return the proxy URL and port number. Is there anyway to return the proxy config only if the port is active and listening for a response, and if not return no proxy settings?

For example:

    function FindProxyForURL(url, host)
{
if (//proxy server is active and contactable)
return "PROXY 192.168.1.1:8080";
else
return "DIRECT";
}