title: <span> with "float: right" inside "white-space: pre"
body: <p>The following HTML:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div style="white-space: pre"&gt;
    long time; &lt;span style="float: right;"&gt;// know C?&lt;/span&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>renders differently in WebKit and Gecko. With WebKit, the contents of the span remain on the same line as the preceding text, but with Gecko, they are moved to a new line.</p>
  
  <p><strong>Which behaviour is correct, and why?</strong></p>