I can't believe Mozilla would do such a thing, but as a designer I am on Metalab's side, it is unacceptable that any company would do such a thing. Mozilla needs to issue an apology and pay for the design if the intend to clear in any way what they have done.
It is also sad that a talented team like mozilla's couldn't come up with an idea of their own or at least pay for it.
On another note, is there a way for Metalab to take legal actions towards Mozilla?