About XUL

XUL was an XML UI declarative language used by Firefox and other Mozilla products until 2017 (Firefox 57). It allowed to define a full UI with buttons, panels, text boxes, etc... in XML.

See developer.mozilla.org/en-US/docs/Archive/Mozilla/XUL for more information.

Example

Consider the following XML file:

      <?xml version="1.0"?>
      <?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
      <window id="vbox example" title="Example 3...."
              xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
         <vbox>
            <button id="yes1" label="Yes"/>
            <button id="no1" label="No"/>
            <button id="maybe1" label="Maybe"/>
         </vbox>
      </window>      

This will give the following result: