title: onMouseover not working in Firefox
body: <p>I'm using <code>onmouseover</code> which works in my standard browser but does not seem to work in <em>Firefox</em>. I tried recreating it using <em>jQuery</em> but it still hasn't worked.  </p>
  
  <p>How could I make this compatible with <em>Firefox</em>?</p>
  
  <pre class="lang-js prettyprint-override"><code>if (img_default.style.overflow != 'visible') {
      div.onmouseenter = function() {
        mouseOver(event)
      };
  } else {
      el.style.display = "none";
  }
  
  function mouseOver(event) {
      if (img_default.style.overflow === 'visible') {
          el.style.display = "none";
      } else {
          el.style.display = "inline-block";
          var posX = event.offsetX ? (event.offsetX) : event.pageX - div.offsetLeft;
          var posY = event.offsetY ? (event.offsetY) : event.pageY - div.offsetTop;
          zoom.style.backgroundPosition = (-posX * 1) + "px " + (-posY * 1) + "px";
      }
  }
  </code></pre>
  
  <p><a href="https://jsfiddle.net/f7g5dw4w/5/" rel="nofollow noreferrer">Here</a> is the entire JSFiddle.</p>