Udate.xml konfiguration??

Ich denke auch daß das nur über SSL geht.

http://developer.mozilla.org/en/docs/Settin…n_update_server

The large updates themselves can be safely served from a non-secure server because the update files contain a hash that the client will verify. The hash can be trusted only if the update.xml is served securely.

Ach ja, das hier sollte vielleicht auch nicht ganz uninteressant sein:

Firefox doesn't pay attention to changes made to app.update.url in about:config, because they apply to the profile. Some software update settings,like the update url and channel, must be global so that using multiple profiles don't cause problems.

You need to change the definition of app.update.url in <firefox>\defaults\pref\firefox.js instead.