Javascript

1 
<script>
function adjustWH(value){
  Height =  window.innerHeight || document.body.offsetHeight
  target = value/Height * 100
  if (target < 100) {
  target = 100
  }
  document.getElementById("main").height = (Math.floor(target))+"%"
}
</script>

I need to get the previous script to work in firefox (its allready working in IE) is there anything i should pay attention to?