GM_setValue("test", 0);
alert(GM_getValue("test")); // Ok
window.addEventListener("DOMSubtreeModified", function(e) {
    window.removeEventListener(e.type, arguments.callee, false);
    alert(GM_getValue("test")); // Ошибка: Greasemonkey access violation: unsafeWindow cannot call GM_getValue.
}, false);

// Examines the stack to determine if an API should be callable.
function GM_apiLeakCheck(apiName) {
  var stack = Components.stack;

  do {
    // Valid stack frames for GM api calls are: native and js when coming from
    // chrome:// URLs and the greasemonkey.js component's file:// URL.
    if (2 == stack.language) {
      // NOTE: In FF 2.0.0.0, I saw that stack.filename can be null for JS/XPCOM
      // services. This didn't happen in FF 2.0.0.11; I'm not sure when it
      // changed.
      if (stack.filename != null &&
          stack.filename != gmSvcFilename &&
          stack.filename.substr(0, 6) != "chrome") {
        GM_logError(new Error("Greasemonkey access violation: unsafeWindow " +
                    "cannot call " + apiName + "."));
        return false;
      }
    }

    stack = stack.caller;
  } while (stack);

  return true;
}