Amazon is currently offering 75% off any movie rental in Amazon Video when you use promo code MOVIE75OFF. To use the code, find the movie you want to rent, then click the “More Purchasing Options” link below the price. In the popup that appears, click “Redeem a gift card or promotion code” and enter the promocode in the field provided. Complete the rental purchase and you’ll then be able to watch the movie on the Fire TV or any other Amazon Video device.