Been trying out
Flock, a weird upcoming browser based on Firefox 1.5 It seems cool, good for bloggers and del.icio.us users like me, but it's slow.
Anyway, apparently, even though it is
based off of Firefox, it isn't compatible with Firefox extensions. (seems like a bad marketing decision to me)
Just giving a heads up. If Flock kicks off and becomes popular, you may find yourself making an extension for it.