Firefox resets Javascript's variable's value

   build: function() {
       var progressCount = 0; 
       var otherFunction = function(number) {
               alert(number);
       } ;
       var finalFunction = function() {
               alert("done");
       } ;
       var progress = function() {
               alert(progressCount);  // very important line!
               progressCount++;
               otherFunction(progressCount);
               if (progressCount == ARRAY.length) {
               finalFunction();
               }
       };
       ARRAY=document.getElementsByClassName("picture");
       for (var i = 0; i < ARRAY.length; i++)
       ARRAY[i].addEventListener("load", progress);
   }

I'm using an onload eventlistener to call a script which increases the value of a variable. I need to get the variable's value before I increase it. Safari and Chrome (Webkit) give the right result but Firefox always alerts "0"... To be clear: Firefox also alerts "done" which means it gets the job done but it does NOT alert the right value before I increase it! This is my Script: var obj = { build: function() { var progressCount = 0; var otherFunction = function(number) { alert(number); } ; var finalFunction = function() { alert("done"); } ; var progress = function() { alert(progressCount); // very important line! progressCount++; otherFunction(progressCount); if (progressCount == ARRAY.length) { finalFunction(); } }; ARRAY=document.getElementsByClassName("picture"); for (var i = 0; i < ARRAY.length; i++) ARRAY[i].addEventListener("load", progress); } } obj.build(); What else could I try? Thank you very much!