fune/js/xpconnect/tests/browser/browser_realm_key_promise_top.html

<script type="text/javascript">
document.domain = "mochi.test";
window.P = new Promise(r => r(10));
</script>
<iframe src="http://test2.mochi.test:8888/browser/js/xpconnect/tests/browser/browser_realm_key_promise_frame.html">
</iframe>
<span id="result"></span>