Why is the code execution order different in Chrome and Firefox?

Question

JavaScript

Code like this:

<script>
  setTimeout(function() {
    alert('setTimeout-1')
  }, 0);
  setTimeout(function() {
    alert('setTimeout-2')
  }, 0);
  setTimeout(function() {
    alert('setTimeout-3')
  }, 0);
</script>
<p>paragraph-1</p>
<script>
  alert('one');
</script>
<p>paragraph-2</p>
<script>
  alert('two');
</script>
<p>paragraph-3</p>
<script>
  alert('three');
</script>
<p>paragraph-4</p>
<script>
  alert('four');
</script>

In Firefox, alert (one, two, three, fout) is executed first, and only then the setTimeout callback function is called. But in Chrome, first alert(one and two), then callback functions, and only then everything else. Why is this happening?