I'm afraid I couldn't quite follow your suggestions, however. If you enable romaji display in the settings and look at a work like テスト you should see "tesuto" in the popup and also when you copy the entry.
(Note that the extension will not work on addons.mozilla.org because Firefox blocks extensions from working there.)
Could you please email me at info@birchill.co.jp to let me know what is missing. Thank you!
