I just restart firefox once in a while, and it updates then. Never seen Firefox hollerin' anything about updates. I've got it set to auto update though. Perhaps if you chose an option other than "Check for updates, but let me choose whether to install them" it'd be quiet. It's in Tools->options->advanced->updates.
If you're talking about the Flash plug-in update, that's a problem you can blame on Adobe for releasing something more insecure than IE. Talk about something that goes through more versions than Firefox.... that'd probably be it.