XMLHttpRequest POST and open target page in new window/tab

Question

How do you emulate Form's 'POST' action with target="_blank" in XMLHttpRequest? (ie post data and open target page in a new tab)

Answer 1

gBrowser offers this functionality right out of the box.

var dataStream = Cc["@mozilla.org/io/string-input-stream;1"].createInstance(Ci.nsIStringInputStream);
dataStream.data = "foo=bar&alpha=beta"; // make sure the values are properly encoded with encodeURIComponent

var postStream = Cc["@mozilla.org/network/mime-input-stream;1"].createInstance(Ci.nsIMIMEInputStream);
postStream.addHeader("Content-Type", "application/x-www-form-urlencoded");
postStream.addContentLength = true;
postStream.setData(dataStream);

gBrowser.loadOneTab("http://www.example.com/", {inBackground: false, postData: postStream});