PAC file

auto.pac

function regExpMatch(url, pattern) {
        try { return new RegExp(pattern).test(url); } catch(ex) { return false; }
}

function FindProxyForURL(url, host) {
        if (shExpMatch(url, "*twitter.com*")) return 'SOCKS 127.0.0.1:6789';
        if (shExpMatch(url, "*facebook.com*")) return 'SOCKS 127.0.0.1:6789';
        if (shExpMatch(url, "*youtube.com*")) return 'SOCKS 127.0.0.1:6789';
        return 'DIRECT';
}