title: CSS fixed position movement under scrollbar in Firefox
body: <p>In Firefox (version 19.0.2) when positioning an element to the right of the page using <code>position: fixed</code> the element is positioned relative to the window viewport right of the window scrollbar. </p>
  
  <p>However, on hover when we change the positioning values, the element is positioned relative to the window viewport not including the window scrollbar. </p>
  
  <p>In the following example this causes the element to move from right of the scrollbar, to underneath the scrollbar on hover.</p>
  
  <p>I have isolated the problem down to see that it is not caused by any other css settings set on <code>body</code>, <code>html</code> or anything else, but I cannot find the reason for this problem.</p>
  
  <p><strong>HTML</strong></p>
  
  <pre><code>&lt;a href="#Top" id="ScrollToTop"&gt;Top&lt;/a&gt;
  </code></pre>
  
  <p><strong>CSS</strong></p>
  
  <pre class="lang-css prettyprint-override"><code>#ScrollToTop {
      position: fixed;
      right: 0px;
      bottom: -10px;
      width: 50px;
      height: 50px;
      background: #ffffff;
      color: #000000;
  }
  #ScrollToTop:hover {
      bottom: 0;
  }
  </code></pre>
  
  <p><strong><a href="http://jsfiddle.net/KxEUY/" rel="nofollow">Example</a></strong></p>
  
  <p>Is there a reason this is occurring? Is this a browser bug? Is there a way to fix this case?</p>