100% Fake. This was from a malvertising Ad on a site you were viewing. This was Not from Mozilla or the Firefox web browser. They claim you can get a iPhone X, Samsung S8 or S9 or a $1000 gift card from say Amazon. This is a scam to try and trick people into giving details like name, address, email, phone# and credit card information to supposedly pay for the cheap $1 shipping. Really, $1 shipping for a phone that is several hundred plus US dollars. Mozilla has never had expensive prizes from random websites though they have done some prizes like limited edition t-shirts in a few occasions to say extension developers.