Add-on SDK bug whereby EventListener interfaces passed to addEventListener() don't get properly wrapped/proxied events

addon-sdk-eventlistener-bug.js

var myListener = {
  handleEvent: function(event) {
    // This produces e.g. [object XrayWrapper [object HTMLHtmlElement]],
    // instead of [object HTMLHtmlElement].
    console.log(event.target);
  }
};

document.addEventListener("mouseover", myListener, true);