tooltip not working

I'm using this code in *.xul

<tooltip id="tt">
  <label value="additional information"/>
</tooltip>

<statusbar id="status-bar">
<statusbarpanel id="mypanel" tooltip="tt"
    label="my panel"
  />
</statusbar>

I don't know why but when I'm over mypanel with 开发者_JAVA百科mouse. There is no popup window with "additional information"

thank you for help

---

I'm not sure, but this might be because the <tooltip> element needs to be inside of a <popupset> element. By the way, you shouldn't use the statusbar anymore; use the add-on bar instead: https://developer.mozilla.org/en/The_add-on_bar