Weird assumption - that Mozilla liked them and would have given them work in the future if he would not have complained. Though, I agree that it probably could have been resolved out of the public's view.
Why is it a weird assumption? Their blog post shows an e-mail from Daniel (the person they are lambasting) that says "Your company has first-class UI/graphics design chops and I will certainly keep MetaLab in mind when bidding out future projects that require such services."
Boilerplate perhaps, but generally if a company is willing to rip off your designs for use in their own internal concepts, I would take that as a sign that they like what you are doing.
I mean, I think this whole thing is stupid, but if they've shown they'll do it once, what's to stop from doing it again? Why would they hire you after that?
No one is saying that they shouldn't have complained... what some are arguing is that they should have complained directly to Mozilla instead of the Internet at large. By making their complaint (valid as it is) so public, they've risked any possibility that they could get design work from Mozilla in the future. A quick email to say, ?Hey, we noticed that the design of this tool that's in development was copied from our design" would have done the trick. Instead of riling up designers online, this could have been handled much better.