title: changing the content of browser in XULRunner
body: <p>I have an Xulrunner app that loads fullscreen without any controls and loads a html page by default. The only thing it has is browser element and a popup menu visible on right click. 
  In the popup menu there is option to quit. Then there is a menu entry 'theme2'. I want the browser to load another html when theme2 is clicked.</p>
  
  <p>This is my main.xul, thats loaded by default:</p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;?xml-stylesheet href="chrome://global/skin/" type="text/css"?&gt;
  &lt;window id="main" title="Edusoft" hidechrome="true" sizemode="maximized" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"&gt;
  &lt;script type="application/x-javascript"&gt;
  function do()
  {
   var browser1 = document.getElementById('browser');
   browser1.loadURI("chrome://myapp/content/theme2/home.html");
  }
  &lt;/script&gt;
  
  &lt;browser id="browser" type="content" src="chrome://myapp/content/theme1/index.html" flex="1" context="clipmenu"/&gt;
  
  
  
  &lt;popupset&gt;
    &lt;menupopup id="clipmenu"&gt;
         &lt;menuitem label="About Us"/&gt;
      &lt;menuseparator/&gt;
      &lt;menuitem label="Theme2" oncommand="do();"/&gt;
      &lt;menuseparator/&gt;
      &lt;menuitem label="Exit" oncommand="close();"/&gt;
    &lt;/menupopup&gt;
  &lt;/popupset&gt;
  
  &lt;/window&gt;
  </code></pre>
  
  <p>I tried this, but when the page is loaded this way.. the popup menu is nomore in the new page.</p>
  
  <pre><code>window.location.assign()
  </code></pre>
  
  <p>There is something like <code>loaduri()</code>, but i have no idea on how to use it.</p>