Neither Mozilla or the Firefox web browser for any device have opportunities to get or win gift cards. This sounds like it could be a scam to get personal information and credit card details. The needing to pay $1 sounds like a scam site that was going on for a while trying to trick some android and desktop Firefox users in claiming they can get a new iPhone X for only just a $1 and giving personal details and credit card info. The two images below are examples of the mentioned iPhone X for a $1 scam so the $1000 gift card for a $1 sounds to be of same scam concept. You may want to contact you credit card company about the charges and to watch the card or get new one.