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XUL which is pronounced zool stands for XML User Interface Language is a Mark-up language used primarily in Mozilla applications. It allows for the creation of feature rich visually appealing cross platform applications to be easily created and maintained for online or offline use.


XUL is an XML language and thus has the advantages of being cross-platform also allows for the insertion of other XML languages into it such as XHTML, MathML and SVG. Also because of its localized structure it can be easily translated into other languages.

XUL is often used for creating Mozilla extensions, such as ChatZilla. Web applications can and do utilize XUL, but these are rare (typically proof-of-concept, such as the Mozilla Amazon Browser). These XUL-based web applications can be confused for a native desktop application as they share many similar graphical widgets (text box, button, label, list box, check box, tree, menu, toolbar and more).

Tip: If a web application is the goal, it is wise to use XUL with the XMLHttpRequest JavaScript object to make a responsive, "snappy" application that not only looks like a desktop application, but acts likes one speed-wise.

Standalone XUL applications are more popular than web-based ones as the browser restricts operations (due to security concerns). When developers seek to add more functionality, a XUL application can be installed locally and will utilize Chrome so that it may be granted elevated privileges.

Currently, an application named XULRunner is being developed that will offer a runtime environment for XUL applications.

Common Usages

  • Textboxes and inputs
  • Toolbars and buttons
  • Navigation menus
  • Tabbed windowing systems
  • Keyboard Mnemonics and input handling

Supported Technologies

  • HTML 4.0 and XHTML
  • CSS2 and some of CSS3
  • DOM2 and some of DOM3
  • XML
  • MathML
  • RDF
  • XSLT
  • XPath
  • Simple XLinks
  • XPointer
  • XML Base
  • FIXPtr
  • SOAP (Simple Object Access Protocol)
  • WSDL (Web Services Description Language)
  • ECMAScript/Javascript
  • XBL (eXtensible Bindings Language)
  • GIF, JPG, PNG, BMP, ICO images
  • HTTP 1.1

Sample Code

<?xml version="1.0"?>
<?xml-stylesheet href="chrome://global/skin" type="text/css" ?>
<window xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
        align="center" pack="center" flex="1">
  <description>Is XUL cool or what?</description>
    <radio id="yes" selected="true" label="Yes!"/>
    <radio id="no" label="No wai"/>
  <button id="dpsbutton" label="DPS909 is fun" />

Example Applications

  • Mozilla Amazon Browser (MAB) - Rich web application that allows for searching of Amazon's content across their 6 websites (US, Canada, UK, Japan, Germany and France). Can be used through the web or downloaded to the desktop.
  • XUL Periodic Table - Demonstrates many of the visual capabilities of XUL.

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