title: Firefox html ordered list numbering messed up by sublist
body: <p>My sublists suddenly started breaking my ordered lists in Firefox (68.0.2) for Ubuntu, and Firefox on my android mobile.  Is this a Firefox bug or is my syntax bad here?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;ol&gt;
    &lt;li&gt;Ordered list item 1&lt;/li&gt;
    &lt;ul&gt;
      &lt;li&gt;sub bullet list item&lt;/li&gt;
      &lt;li&gt;sub bullet list item&lt;/li&gt;
      &lt;li&gt;sub bullet list item&lt;/li&gt;
      &lt;li&gt;sub bullet list item&lt;/li&gt;
      &lt;li&gt;sub bullet list item&lt;/li&gt;
    &lt;/ul&gt;
    &lt;li&gt;Ordered list item #2. Why is this appearing as 6 in Firefox?&lt;/li&gt;
  &lt;/ol&gt;</code></pre>
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  </p>