It's still irresponsible to use those images and that layout, after rejecting a bid by that design company to create images and layout for the product, even in a mockup.
It is irresponsible, for sure. But is an appropriate reaction to set up a big witch hunt and publicly shame Mozilla? Is that how businesses and organizations should be treating each other? People make mistakes. Give them a chance to make things right before you try to do damage to someone's reputation.
It's still irresponsible to use those images and that layout, after rejecting a bid by that design company to create images and layout for the product, even in a mockup.