V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

XUL
       XML-based User interface Language (XML, Netscape, Mozilla, AOL)


The Free On-line Dictionary of Computing (30 December 2018):

XML User-Interface Language
XUL

    (XUL) An XML-based language created for the
   Mozilla browser for development of cross-platform user
   interfaces.  XUL supports input controls such as
   textboxes and checkboxes, toolbars, menus, dialogs,
   trees, keyboard shortcuts, and more.

   XULPlanet (http://xulplanet.com/).

   (2003-06-14)