--main.xul

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>

<window
   id="main"
   title="Test"
   width="1280"
   height="1024"
   xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
>
   <script src="main.js"/>   
   <browser flex="1" id="main_browser" src="file://d:/test.html"/>
</window>

--main.js

function onLoad() {
   var main_browser = document.getElementById("main_browser");
      
   window.fullScreen = true;
   main_browser.loadURI("file://d:/test.html", null, null);
}

addEventListener("load", onLoad, false);