Slideshow works with Firefox but not with Safari

Slideshow works with Firefox but not with Safari

Hi there!
I have a - i think - simple question.
I made a simple Slideshow with this tutorial:
http://tutorialzine.com/2009/11/beautiful-apple-gallery-slideshow/
Not exactly the same, but the basic functions are from this script.

Here's the script for the slideshow:
  1. $(document).ready(function(){
  2.     var totWidth=0;
  3.     var positions = new Array();
  4.     $('#slides .slide').each(function(i){       
  5.         positions[i] = totWidth;
  6.         totWidth += $(this).width();       
  7.     });
  8.    
  9.     $("#slides").width(totWidth);
  10.    
  11.     $("#slidemenu ul li a").click(function(e){
  12.         var pos = $(this).parent().prevAll(".menuItem").length;
  13.         $("#slides").animate({marginLeft: -positions[pos]+"px"});
  14.         e.preventDefault();
  15.     });
  16. });
i also tried to travel through the DOM to get to the right div, but it didn't help..
The funny thing is, that any other div, except the #slides-div can be animated, and it works perfect with Firefox..
You can have a look at this slideshow here:
Slideshow

Maybe you can help me with this problem,
Greets,
Markus