Is 'DOMFocusIn' supported?

I see the 'DOMFocusIn' event type listed on two pages on DMO:

https://developer.mozilla.org/en/DOM_Events#DOMFocusIn
https://developer.mozilla.org/en/DOM_Client_Object_Cross-Reference/DOM_Events

I see it also listed in the event list of the Event Spy [1] extension.

I bascially have an HTML page with some focusable elements (form 
controls, hyper-links) and register an event handler on the 
#document node like:

document.addEventListener("DOMFocusIn", myHandler, false);

My event handler gets never invoked.  The same thing appears to work 
in Opera and Safari.  Is 'DOMFocusIn' supported and specifically in 
web pages?

[1] https://addons.mozilla.org/addon/1100/

-- 
Stanimir