Ref: http://mxr.mozilla.org/mozilla-central/source/toolkit/mozapps/extensions/AddonManager.jsm#1407

If we write code properly, Firefox will auto-install updates for us. There's also a pref extensions.update.autoUpdateDefault I believe, that controls this.

Details need to be determined, but we should probably default to acting like Firefox does for extensions.