keypress is not working in Mozila Firefox

Question

I have got a task to restrict textbox from alphabetic values. Only floating point values are possible. After the decimal we have to write out two digits. I did this but it does

Answer 1

function isNumberKey(evt) { 
     var charCode = (evt.charCode) ? evt.which : event.keyCode

     if (charCode > 31 && (charCode < 48 || charCode > 57) && charCode != 46) 
         return false; 
     else { 
         var len = document.getElementById("txtChar").value.length; 
         var index = document.getElementById("txtChar").value.indexOf('.'); 

         if (index > 0 && charCode == 46) { 
             return false; 
         } 
             if (index >0 || index==0) { 
                 var CharAfterdot = (len + 1) - index; 
                 if (CharAfterdot > 3) { 

                     return false; 
                 } 

}

         } 
         return true; 
      }