HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>MozMousePixelScroll detail</title>
  <style>
    #box { height: 160px; overflow: auto; border: 2px solid #333; padding: 12px; }
    #box p { height: 400px; margin: 0; }
  </style>
</head>
<body>
  <p>Legacy Firefox only — may stay quiet in Chromium/Safari.</p>
  <div id="box"><p>Scroll me with the mouse wheel.</p></div>
  <pre id="out">(waiting)</pre>
  <script>
    var box = document.getElementById("box");
    var out = document.getElementById("out");
    box.addEventListener("MozMousePixelScroll", function (event) {
      var dir = event.detail < 0 ? "toward bottom/right" : "toward top/left";
      out.textContent = "detail=" + event.detail + " (" + dir + ")";
    });
  </script>
</body>
</html>

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Element MozMousePixelScroll — detail direction (Try It)