title: Changing scrollTop does not continue inertia scrolling
body: <p>I have a div with scrollable content that at a certain scrollTop value goes back to top.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var container = document.getElementById('container');
  
  function scroll_function() {
  
    var new_position_top = container.scrollTop;
  
    if (new_position_top &gt; 600) {
  
      container.scrollTop = 0;
  
    }
  
  }
  
  container.addEventListener('scroll', scroll_function);</code></pre>
  <pre class="snippet-code-css lang-css prettyprint-override"><code>#container {
    width: 300px;
    height: 300px;
    overflow: auto;
    border: 1px solid black;
    -webkit-overflow-scrolling: touch;
  }
  span {
    width: 100%;
    height: 1200px;
    float: left;
    background: red;
    background: -webkit-linear-gradient(red, yellow);
    background: -o-linear-gradient(red, yellow);
    background: -moz-linear-gradient(red, yellow);
    background: linear-gradient(red, yellow);
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div id="container"&gt;
    &lt;span&gt;&lt;/span&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p><a href="https://jsfiddle.net/5gtvezth/1/" rel="nofollow noreferrer">JSFiddle</a>.</p>
  
  <p>Using a MacBook trackpad I am getting different behaviours:
  Chrome and Safari work as I would expect, continuing the inertia after going back to the top.
  <strong>Firefox</strong>, however, goes back to the top and stops the inertia.</p>
  
  <p>Using <strong>iOS Safari</strong> a similar issue appears too, as the scrollTop position is not updated until the inertia finishes.</p>
  
  <p><strong>Is there a better way of approaching it or a way to fix desktop Firefox and iOS Safari behaviour?</strong></p>