Why doesn't the following code work in firefox?

Question

JavaScript

Hello.
Why doesn't the following code work in firefox?

$(".button-map").click( function(event){
  event.preventDefault();
    if ( $(this).hasClass("isDown") ) {
    $("#map > ymaps").stop().animate({"height":500},"slow");	    					
    } else {
        $("#map > ymaps").stop().animate({"height":250},"slow");
    }
    $(this).toggleClass("isDown");
  return false;
});

Answer 1

Don't know, works for me: jsfiddle.net/c9kjsbwj