<html>
<head>
<script>
window._secretValue = {answer:42};

window.getUniqueValue = function() {
    if (!window._cachedUniqueValue)
        window._cachedUniqueValue = Math.floor(Math.random() * 10e9);

    return window._cachedUniqueValue;
}

function initialize() {
    document.getElementById("uniqueValueField").innerText = window.getUniqueValue();
};
</script>
<body onload="initialize()">
<h1>This is a test extension.</h1>
<p>In a normal extension, this area would show the extension's user interface.</p>
<p>The unique value for this iframe's execution context is:
    <span id="uniqueValueField">TBD</span>
</p>
</body>
</html>