.data() is empty when using firefox (latest) and jquery 1.11.1

.data() is empty when using firefox (latest) and jquery 1.11.1

I've this html element

  1. <li data-week="20141103" data-year="2014">
  2.                             <a href="#">
  3.                                 03/11/2014                            </a>
  4.                         </li>


When user click on it I log $(this) to the console. And $(this) is the LI html element.

As you can see, there is a data-week attrbute

If I do

  1. console.log ( $(this).data("week") );

nothing will be printed.


I added a breakpoint using firebug, and added the expression as control expression and Firebug told me


$(this).data("week")                 TypeError: this.__FireQueryShared is undefined

What does it mean?
Why Firefox cannot read my data value ?

This code works well on IE, Chrome, Safari, and Opera.