title: preventDefault blocks right-click menu in Firefox on Mac but not Windows
body: <p>I have a web application in which I have hooked mouse up and mouse down events; I use them for selection and manipulation of the graphical language for which my application is an editor. To prevent the right-click/context menu supplied by Firefox from showing up, I've placed:</p>
  
  <pre><code>if (evt.preventDefault) {
    evt.preventDefault();
  }
  </code></pre>
  
  <p>at the top of each of my mouse up and mouse down event handlers. I don't want to return false; I actually want the event to propagate. </p>
  
  <p>On the Mac, the right-click menu doesn't show up; this is what I expect. On Windows, however, it stubbornly appears, even though Firebug confirms that my call to "preventDefault" is occurring and likewise "defaultPrevented" gets set to true. </p>
  
  <p>Any idea what gives? Has anyone else run across this problem? I'm running Firefox 6.0.2 on both the Mac and Windows.</p>
  
  <p>[Update: more recent versions of Firefox yielded consistent results on Mac and Windows: the context menu failed to be suppressed on both platforms.]</p>