template tree for filesystem not working

I have posted this on mozilla.dev.extensions and received no answer.
It should fit in this more specific group.

Hi,

I took the example from https://developer.mozilla.org/en/XUL_Tutorial/Trees_and_Templates

Actually, nothing is displayed inside the tree.
Can someone tell me what else I should add to the code for it to work.

<tree id="my-tree" flex="1"
       datasources="rdf:files" ref="file:///" flags="dont-build-
content">
  <treecols>
    <treecol id="Name" label="Name" primary="true" flex="1"/>
    <splitter/>
    <treecol id="Date" label="Date" flex="1"/>
  </treecols>

    <template>
      <rule>
        <treechildren>
          <treeitem uri="rdf:*">
            <treerow>
              <treecell label="rdf:http://home.netscape.com/NC-
rdf#Name"/>
              <treecell label="rdf:http://home.netscape.com/WEB-
rdf#LastModifiedDate"/>
            </treerow>
          </treeitem>
        </treechildren>
      </rule>
    </template>
</tree>

Thank you for your help.
(firefox 3.0.3)