<listbox> and <tree> are powerful widgets in the XUL bestiary. They are like form elements on steroids. <listbox> is a little fragile, and <tree> a little complicated, but they are both flexible display systems for serious data-oriented applications.
Even so, you can only go so far displaying static data. The alternative of scripting up content changes using the DOM is bulky, slow, and awkward. For dynamic data, something new is required. Templates are that new technology, and they are discussed next.