This offer is not limited to those with Kindle with Special Offers, but is open to anyone with a Mastercard (but ends at midnight tonight, Pacific Time (US).
Save $10 when you spend $100 on Electronics and Toys with your MasterCard® card at Amazon.com. Plus, get an additional $10 discount on a future purchase.
When you click thru the link above, you'll see a group discount code. Use this promo code during checkout, AFTER you set your payment method to any Mastercard; uou must use the full checkout process in order to enter your promotional code (no one-clicking). Also, like all Amazon sales that use promotional codes, if you have a gift card balance, you must use it for the payment - if you have more than a $100 balance, you may need to call and have your gift balance frozen while you enter the order; if you have less, whatever is there is used up first (so, you could put, say $89 on your Visa and apply it to your account as a gift card, then pay the remainder using your Mastercard).
Just like the last offer, you can use this one on the Kindle Fire; you'll get the $10 off $50 bonus by email within 30 days and can use it on any product sold "by Amazon.com", which should also include gift cards. Don't be fooled by the limited selection on the Special Offer page, either - you can click on More in Electronics or More in Toys and get about 70,000 more items.