<html>
    <embed id="launcher" type="application/x-embedded-emacs-launcher" />
    <script type="text/javascript" src="/background.js"></script>
</html>

<html>
    <embed id="launcher" type="application/x-embedded-emacs-launcher">
    <script type="text/javascript" src="/background.js"></script>
</html>

Drop trailing slash in <embed>
Drop trailing slash in <embed>

No need for it; <embed> is a void element.
