I can agree this is really a special and cute Firefox T-shirt created by: pacopanda
I did not know that he have started to make cute T-shirt. I thought he only did mugs but it is nice that he have start whit this thing to. Should be nice to see what more t-shirt prints he is going to release in the future.
You can bought it here: http://www.redbubble.com/people/pandapaco/works/10447911-cute-firefox and it is available in different sizes and colors, also available V-neck, long sleeve and hoodies.
You find his store here if you wont to bought something else and i hope that he is going to release more nice print soon. I am thinking about to bought this one.