Hi,
Instead of deleting the update service, you can simply disable it by adding two configuration files:
1) c:\Program...\Mozilla Firefox\mozilla.cfg :
lockPref("app.update.enabled", false);
lockPref("app.update.service.enabled", false);
2) c:\Program...\Mozilla Firefox\defaults\pref\autoconfig.js :
pref("general.config.filename", "mozilla.cfg");
pref("general.config.obscure_value", 0);
Regards