Submit button not working on Firefox

[(--eRRoR--)]

So helo there all.
I aplyed a java script to an php file i have to prevent users pressing to many times on a button in my web shop.
The script works perfect in Chrome.I Firefox it does this.


Here is the code

<SCRIPT LANGUAGE="JavaScript" TYPE="text/JavaScript">
function formControl(submitted) 
{
   if(submitted=="1") 
    {
   commentForm.Submit.disabled=true
   //alert("Processing,please wait...")
    } 
}
</SCRIPT>

       echo '<FORM action="" method="post" enctype="text/plain" name="commentForm">';
echo '<input type="submit" name="Submit" onclick="javscript:location.href=\'./buy.php?v1='.$v1.'&v2='.$v2.'&co='.$item.'\';formControl(1);" value=\'Yes I am\'>';
      echo '<input type="button" onclick="javscript:location.href=\'./webshop.php?v1='.$v1.'&v2='.$v2.'\'" value=\'No I`m not\'>';
      echo '</FORM>';