http://www.xulplanet.com/reference/elemref/ref_listheader.html A header for a single column in a listbox. Indicates whether the listheader is disabled or not. If this attribute is set to true, the listheader is disabled. This is usually drawn with the text in grey. If the listheader is disabled, it does not respond to user actions. The element cannot be focused and the command event will not fire. The element will still respond to mouse events. To enable the listheader, leave the attribute out entirely as opposed to setting the value to false.