This offers examples of sending POST data to the server and displaying the server response.
Need more elaborate examples, examples of displaying the response in a new tab, in background tabs, and a link to using XMLHttpRequest for POST requests.
Preprocessing POST data
The aPostData argument of the (global) loadURI(), openDialog(), and (tab)browser.loadURIWithFlags() methods expects the POST data in the form of an nsIInputStream (because they eventually call nsIWebNavigation.loadURI()) while POST data can be created using nsIMIMEInputStream. Most of the time, POST data starts as a data string in the form of "name1=data1&name2=data2&...", so you must convert it before passing the data to one of the methods. Here is an example:
var dataString = "name1=data1&name2=data2";
// POST method requests must wrap the encoded text in a MIME
// stream
const Cc = Components.classes;
const Ci = Components.interfaces;
var stringStream = Cc["@mozilla.org/io/string-input-stream;1"].
createInstance(Ci.nsIStringInputStream);
if ("data" in stringStream) // Gecko 1.9 or newer
stringStream.data = dataString;
else // 1.8 or older
stringStream.setData(dataString, dataString.length);
var postData = Cc["@mozilla.org/network/mime-input-stream;1"].
createInstance(Ci.nsIMIMEInputStream);
postData.addHeader("Content-Type", "application/x-www-form-urlencoded");
postData.addContentLength = true;
postData.setData(stringStream);
// postData is ready to be used as aPostData argument
...
POSTing data to the current tab
There is a convenience method in global scope (in Firefox, chrome://browser/content/browser.js):
loadURI(aURI, aReferrer, aPostData, aAllowThirdPartyFixup);
POSTing data to a new window
window.openDialog('chrome://browser/content', '_blank', 'all,dialog=no',
aURI, aFlags, aReferrer, aPostData);