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https://bugzilla.mozilla.org/show_bug.cgi?id=856384
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  <title>Test for Bug 856384</title>
  <script src="/tests/SimpleTest/SimpleTest.js"></script>
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<body>
<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=856384">Mozilla Bug 856384</a>
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<iframe name="constructor" src="about:blank"></iframe>
<pre id="test">
<script type="application/javascript">
SimpleTest.waitForExplicitFinish();

function run()
{
  is(Object.isExtensible(window), true, "Windows are extensible by default");

  try
  {
    Object.preventExtensions(window);
    throw "didn't throw";
  }
  catch (e)
  {
    is(e instanceof TypeError, true,
       "preventExtensions(window) should throw a TypeError, instead got: " + e);
    is(Object.isExtensible(window), true,
       'Windows are extensible after an extensibility "change" attempt');
  }

  SimpleTest.finish();
}

window.addEventListener("load", run);
</script>
</pre>
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