Firefox extension - Display customized popup message just above the status bar

I am new to extension development, I have a requirement wherein I need to do some check开发者_StackOverflow社区ing on the page and display a popup message at the bottom of main window, just above the status bar.

I used the insertAfter attribute with value "browser-bottombox" but this does not display the label at all.

<overlay id="gHook" xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
   <hbox insertAfter="appcontent" height="75" id="glhbox">
      <label value="Sup Message"></label>
   </hbox> 
</overlay>

This does not display any thing.

Help much appreciated. Thanks

Depending on how "customised" you need it to be, the notify box might do what you want:

https://developer.mozilla.org/en/XUL_School/User_Notifications_and_Alerts