Perhaps IE is refusing to let Windows handle the "xfire" protocol? Have you tried using a standard link in IE, e.g.:
<a href="xfire:status?text=test">Click here</a> to change your status text!</a>
Does that work in IE? If so, you might need to redirect the user to this link via a META refresh tag, or perhaps some Javascript (as well as a standard link for those who don't have JS enabled, of course).