var msgWindow = Components.classes["@mozilla.org/messenger/msgwindow;1"].createInstance(Components.interfaces.nsIMsgWindow);

    var content = "";
    var MsgService = messenger.messageServiceFromURI(mURI);
    var MsgStream =  Components.classes["@mozilla.org/network/sync-stream-listener;1"].createInstance();
    var consumer = MsgStream.QueryInterface(Components.interfaces.nsIInputStream);
    var ScriptInput = Components.classes["@mozilla.org/scriptableinputstream;1"].createInstance();
    var ScriptInputStream = ScriptInput.QueryInterface(Components.interfaces.nsIScriptableInputStream);
    ScriptInputStream.init(consumer);
    try {
      MsgService.streamMessage(mURI, MsgStream, msgWindow, null, false, null);
    } catch (ex) {
      alert("error: "+ex)
    }
    ScriptInputStream.available();
    while (ScriptInputStream.available()) {
      content = content + ScriptInputStream.read(512);
    }
    alert(content);

var Cc = Components. classes;
var Ci = Components. interfaces;
function getDirectory ()
{
	var prefs = Cc ["@mozilla.org/preferences-service;1"].
		    getService (Ci. nsIPrefService).
		    getBranch ("custombuttons.buttons.saveSelected.");
	var fp = Cc ["@mozilla.org/filepicker;1"].
		 createInstance (Ci. nsIFilePicker);
	try
	{
		var folder = prefs. getComplexValue ("lastFolder", Ci. nsILocalFile);
		fp. displayDirectory = folder || null;
	} catch (e) {}
	fp. init (window, "", fp. modeGetFolder);
	var res = fp. show ();
	if (res != fp. returnOK)
		return null;
	prefs. setComplexValue ("lastFolder", Ci. nsILocalFile, fp. file);
	return fp. file;
}
function saveAsFile (uri, dir)
{
	var content = "";
	var subject = messenger. messageServiceFromURI (uri).
		      messageURIToMsgHdr (uri). mime2DecodedSubject;
	filename = GenerateValidFilename (subject, ".eml");
	var msgService = messenger. messageServiceFromURI (uri);
	var msgStream =  Cc ["@mozilla.org/network/sync-stream-listener;1"]. createInstance ();
	var consumer = msgStream. QueryInterface (Ci. nsIInputStream);
	var scriptInput = Cc ["@mozilla.org/scriptableinputstream;1"].
			  createInstance ();
	var scriptInputStream = scriptInput. QueryInterface(Ci. nsIScriptableInputStream);
	scriptInputStream. init (consumer);
	try
	{
		msgService. streamMessage (uri, msgStream, msgWindow, null, false, null);
	}
	catch (ex)
	{
		alert("error: "+ex)
	}
	scriptInputStream. available ();
	while (scriptInputStream. available ())
	{
		content = content + scriptInputStream. read (512);
	}
	var subject = msgService. messageURIToMsgHdr (uri).
		      mime2DecodedSubject;
	var fileName = GenerateValidFilename (subject, ".eml");
	var file = dir. clone ();
	file. append (fileName);
	if (file. exists ())
		file. createUnique (Ci. nsIFile. NORMAL_FILE_TYPE, 0664);
	var foStream = Cc ["@mozilla.org/network/file-output-stream;1"].
		       createInstance (Ci. nsIFileOutputStream);
	var flags = 0x02 | 0x08 | 0x20;
	foStream. init (file, flags, 0664, 0);
	foStream. write (content, content. length);
	foStream. close ();
}
var dir = getDirectory ();
if (!dir)
	return;
var messageArray = GetSelectedMessages();
for (var i = 0; i < messageArray. length; i++)
	saveAsFile (messageArray [i], dir);

try
{
	var gIOService = Components. classes ["@mozilla.org/network/io-service;1"].
			 getService (Components. interfaces. nsIIOService);
	var uri = gIOService. newURI ("mailto:recipient@mail.com", null, null);
	var sMsgComposeService = Components. classes ["@mozilla.org/messengercompose;1"].
				 getService (Components. interfaces. nsIMsgComposeService);
	var params = sMsgComposeService. getParamsForMailto (uri);
	params. composeFields. from = "user@mail.com";
	params. composeFields. subject = "any subject";
	params. composeFields. body = "\nany message";
	params. composeFields. forcePlainText = true;
	params. composeFields. useMultipartAlternative = true;
	var am = Components. classes ["@mozilla.org/messenger/account-manager;1"].
		 getService (Components. interfaces. nsIMsgAccountManager);
	var identity = am. createIdentity ();
	identity. fullName = "Full Name";
	identity. email = "user@mail.com";
	var smtpService = Components. classes ["@mozilla.org/messengercompose/smtp;1"].
			  getService (Components. interfaces. nsISmtpService);
	var ss = smtpService. createSmtpServer ();
	identity. smtpServerKey = ss. key;
	ss. hostname = "smtp.mail.com";
	ss. port = 25;
	ss. username = "user"; // *******************
	ss. password = "password"; // ***************
	var msgWindow = Components. classes ["@mozilla.org/messenger/msgwindow;1"].
			createInstance();
	msgWindow = msgWindow. QueryInterface (Components. interfaces. nsIMsgWindow);
	msgWindow. SetDOMWindow (window);
	msgWindow. rootDocShell. allowAuth = true;
	var compose = sMsgComposeService. InitCompose (window, params);
	compose. SendMsg (Components. interfaces. nsIMsgCompDeliverMode. Now, identity, "fakeAccount", msgWindow, null);
}
catch (e)
{
	alert (e);
}

function centerWindowOnScreen() {
    var xOffset = screen.availWidth / 2 - window.outerWidth / 2;
    var yOffset = screen.availHeight / 2 - window.outerHeight / 2;
    xOffset = xOffset > 0 ? xOffset : 0;
    yOffset = yOffset > 0 ? yOffset : 0;
    window.moveTo(xOffset, yOffset);
}

function wait4Load() {
	if(условие выхода из ожидания) {
		return true;
	} else {
		setTimeout(wait4Load(),10000);
	}
}