Uri target = new Uri("http://www.steamcommunity.com/");

cookieContainer.Add(new Cookie("timezoneOffset", "7200,0") { Domain = target.Host });

function setTimezoneCookies()
{
    var now = new Date();
    var expire = new Date();

    // One year expiration, this way we don't need to wait at least one page
    // load to have accurate timezone info each session, but only each time the user
    // comes with cleared cookies
    expire.setTime( now.getTime() + 3600000*24*365 );
    tzOffset = now.getTimezoneOffset() * -1 * 60;
    isDST = 0;
    document.cookie = "timezoneOffset=" + tzOffset + "," + isDST + ";expires="+expire.toGMTString() + ";path=/";
}
// We always want to have the timezone cookie set for PHP to use
setTimezoneCookies();