read and writing file using mozilla xul

Question

I've got a problem with reading and writing files in mozilla xul. At first I want simply to read path to file(to check whether I/O works) So I wrote this code

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" id="window" title="title">
<script>
Components.utils.import("resource://gre/modules/FileUtils.jsm");

var file = FileUtils.getFile("Desk", ["temp.xml"]);
alert(file.path);
</script>
</window>

It should show alert window with path to temp.xml(this file exists on desktop). But it shows nothing in mozilla firefox. what's the problem?

Answer 1

My Firefox shows two problems:

1. it chokes on alert() with error:

   Error: Cannot call openModalWindow on a hidden window = NS_ERROR_NOT_AVAILABLE Source file: resource://gre/components/nsPrompter.js Line: 382

2. Your window has no style, so it's "invisible"

Here is a work around with displaying the path in a textbox instead and in browser console

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<?xml-stylesheet href="chrome://global/skin/global.css"  type="text/css"?>
<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul" id="window" title="title">
    <textbox id="text" value="N/A"/>
<script type="application/javascript">
Components.utils.import("resource://gre/modules/FileUtils.jsm");

var file = FileUtils.getFile("Desk", ["temp.xml"]);
document.getElementById("text").value = file.path;
console.log(file.path);
//alert(file.path);
</script>
</window>