how could I make some IE filter working in firefox

how could I make some IE filter working in firefox ?
my code is :

function change_inc(picture)
{
  picture.src="a_Sample.png";
  logo_opc(picture)
}
function change_dec(picture)
{
  picture.src="p_Sample.png";
  dec_opc(picture)
}

var i = 10; //global variable
var t;
var currentpicture;
function logo_opc(picture){
   if(picture) {
     currentpicture = picture;
   } else {
     picture = currentpicture;
   }
   window.clearTimeout(t);
   if(i<=100){
     picture.filters.item("DXImageTransform.Microsoft.Alpha").opacity = i;
     i++;
     t=window.setTimeout('logo_opc()',10);
   } else return false;
}

function dec_opc(picture){
   if(picture) {
     currentpicture = picture;
   } else {
     picture = currentpicture;
   }
   window.clearTimeout(t);
   if(i>30){
     picture.filters.item("DXImageTransform.Microsoft.Alpha").opacity = i;
     i--;
     window.setTimeout('dec_opc()',10);
   } else return false;
}
// -->
</SCRIPT>


    <IMG id="logo" NAME="m1" SRC="p_Sample.png" BORDER="0" ONMOUSEOVER="change_inc(this)"
            ONMOUSEOUT= "change_dec(this)" STYLE="filter:progid:DXImageTransform.Microsoft.Alpha(opacity=30)">

this is not working in firefox but it do in IE, any help plz ?