McCoy. McCoy is the tool you need to sign your extension's update.rdf if you don't release your app over an SSL link or through addons.mozilla.org. McCoy is simple to download, simple to run (although I recommend 1. a very light installer 2. an app icon, lacking for the time being 3. a direct link to McCoy from addons developer's area 4. a mail to all extension authors about it - or did I miss a mail about it already sent ?), simple to understand, trivial to use. It's a superb small app, efficient and smart, perfectly solving the problem it proposed to solve. And it's yet another excellent example of the power of XULrunner, in case we needed one. Congrats Mossop.