Наблюдатель за загрузкой страницы в настраиваемом браузере xul:

Вы можете попробовать:

var myObserver = {
   observe: function(aSubject, aTopic, aData){
      if (aTopic == 'http-on-modify-request')
              {
                aSubject.QueryInterface(Components.interfaces.nsIHttpChannel);
                var url = aSubject.URI.spec;
                var postData ;
                if (aSubject.requestMethod.toLowerCase() == "post") 
                {
                  var postText = this.readPostTextFromRequest(request);
                  if (postText)
                  {
                    var dataString = parseQuery(postText);
                    postData = postDataFromString(dataString);
                  }
                }

                var oHttp = aSubject.QueryInterface(Components.interfaces.nsIHttpChannel);

                var interfaceRequestor =   oHttp.notificationCallbacks.QueryInterface(Components.interfaces.nsIInterfaceRequestor);
                var DOMWindow = interfaceRequestor.getInterface(Components.interfaces.nsIDOMWindow); 


                //check if it is one of your mini browser windows
                if (jQuery(DOMWindow).hasClass('mini_browser')) 
                {

                  openInTab(url, postData);

                  var request = aSubject.QueryInterface(Components.interfaces.nsIRequest);
                  request.cancel(Components.results.NS_BINDING_ABORTED);

                }

      } 
   },

   QueryInterface: function(iid){
      if (!iid.equals(Components.interfaces.nsISupports) &&
          !iid.equals(Components.interfaces.nsIObserver))
        throw Components.results.NS_ERROR_NO_INTERFACE;

      return this;
   },

   readPostTextFromRequest : function(request) {
     var is = request.QueryInterface(Components.interfaces.nsIUploadChannel).uploadStream;
     if (is)
     {
       var ss = is.QueryInterface(Components.interfaces.nsISeekableStream);
       var prevOffset;
       if (ss)
       {
         prevOffset = ss.tell();
         ss.seek(Components.interfaces.nsISeekableStream.NS_SEEK_SET, 0);
       }

       // Read data from the stream..
       var charset = "UTF-8";
       var text = this.readFromStream(is, charset, true);

       // Seek locks the file so, seek to the beginning only if necko hasn't read it yet,
       // since necko doesn't seek to 0 before reading (at lest not till 459384 is fixed).
       if (ss && prevOffset == 0) 
         ss.seek(Components.interfaces.nsISeekableStream.NS_SEEK_SET, 0);

       return text;
     }
     else {
       dump("Failed to Query Interface for upload stream.\n");
     }
   }
   return null;
 },

 readFromStream : function(stream, charset, noClose)    
 {
    var sis = Components.classes["@mozilla.org/binaryinputstream;1"]
                     .getService(Components.interfaces.nsIBinaryInputStream);

    sis.setInputStream(stream);

    var segments = [];
    for (var count = stream.available(); count; count = stream.available())
      segments.push(sis.readBytes(count));

if (!noClose)   
      sis.close();

    var text = segments.join("");
    return text;
  }
};

function openInTab(url, postData)
{
  var wm = Components.classes["@mozilla.org/appshell/window-mediator;1"]
        .getService(Components.interfaces.nsIWindowMediator);
  var recentWindow = wm.getMostRecentWindow("navigator:browser");
  if (recentWindow) 
  {
    // Use an existing browser window, open tab and "select" it
    recentWindow.gBrowser.selectedTab = recentWindow.gBrowser.addTab(url, null, null, postData);
  } 
}

function parseQuery() {
  var qry = this;
  var rex = /[?&]?([^=]+)(?:=([^&#]*))?/g;
  var qmatch, key;
  var paramValues = {};
  // parse querystring storing key/values in the ParamValues associative array
  while (qmatch = rex.exec(qry)) {
    key = decodeURIComponent(qmatch[1]);// get decoded key
    val = decodeURIComponent(qmatch[2]);// get decoded value

    paramValues[key] = val;
  }
  return paramValues;
}

function postDataFromString(dataString)
{
  // POST method requests must wrap the encoded text in a MIME
  // stream
  var stringStream = Components.classes["@mozilla.org/io/string-input-stream;1"]
               .createInstance(Components.interfaces.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 = Components.classes["@mozilla.org/network/mime-input-stream;1"].
           createInstance(Components.interfaces.nsIMIMEInputStream);
  postData.addHeader("Content-Type", "application/x-www-form-urlencoded");
  postData.addContentLength = true;
  postData.setData(stringStream);

  return postData;
}

Я обновлю это, чтобы немного заполнить пробелы.

изменить: см. http://forums.mozillazine.org/viewtopic.php?p=2772951#p2772951, чтобы узнать, как получить исходное окно запроса.

Запросить код отмены на http://zenit.senecac.on.ca/wiki/index.php/Support_For_OpenID.

см. http://mxr.mozilla.org/mozilla-central/source/netwerk/base/public/nsIRequest.idl для получения подробной информации о nsIRequest.

См. http://forums.mozillazine.org/viewtopic.php?p=2404533#p2404533 и https://developer.mozilla.org/en/XUL/Method/addTab для определения addTab.

parseQuery поступает из http://blog.strictly-software.com/2008/10/using-javascript-to-parse-querystring.html.

См. https://developer.mozilla.org/en/Code_snippets/Post_data_to_window#Post_data_to_window#Post_data_prodata_window# a> о том, как обрабатывать данные публикации в форме, подходящей для addTab.