[Javascript] script no longer working with new FF

[list at tridemail.de (Michael Borchers)]

the following script worked fine for switching several checkboxes, now, i 
guess since the new FF, it stopped working.
some kind of case-sensitive prob?!

<input type="checkbox" name="checkBoxSelect" id="checkBoxSelect" 
onclick="javascript:checkboxSwitch(this, 'whatever');" />


function checkboxSwitch(thisCheckbox, checkboxSubstring)
{
 if(thisCheckbox.checked == true)
 {
  var checked = true;
 }
 else
 {
  var checked = false;
 }

 var checkboxField  = document.getElementsByTagName("input");
 var checkboxFieldLength = checkboxField.length;
 var SubstringLength  = checkboxSubstring.length;

    for(c=0;c<checkboxFieldLength;c++)
 {
  var attributeName  = checkboxField[c].getAttribute("name");
  var attributeNameLength = attributeName.length;
  var SubstringStart  = 
parseFloat(attributeNameLength)-parseFloat(SubstringLength);

  if(attributeName.substring(SubstringStart, attributeNameLength) == 
checkboxSubstring)
  {
   checkboxField[c].checked = checked;
  }
    }
}