====== XML descendants internal method called on incompatible Date ======

I just got this errormessage in [[http://www.getfirebug.com/console.html|Firebug's]] console. What the F? 
What's wrong with this code?

<code javascript>
var d=new Date();
console.info("offset: %s, utc hours: %s", d..getTimezoneOffset(), d.getUTCHours());
</code>

Oops. Notice the two dots before ''getTimezoneOffset''. 

That triggers an [[wp>E4X]] error, which is apparently switched on in the Firebug console...

{{tag>javascript}}