Some of the latest Firefox 3 aka Minefield trunk builds include Growl integration! This is probably a non-event for anyone other than Mac users, but hey Growl notifications without needing to install an extension? Pretty nice.
Get a nightly here: https://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-trunk/
To test Firefox 3 nightlies without possibly messing up your existing profile (preferences, extensions, what have you), use the Profile Manager to create a new profile just for testing. Way less stupid then trying to load up 48 tabs from your current profile in Firefox 3 and then seeing most of the extensions fail to work (which was what I tried to do, once).