A web site promoting free Amazon gift cards was a scam. The catch was that you had to let the page’s countdown reach zero before you would get the free gift card. At first glance, I thought this was going to be a new in-browser miner, but when I opened Fiddler to see the network traffic, I saw instead that the browser was repeatedly connecting to and watching YouTube videos. My guess is that this method is being done to inflate views in the hopes that the higher view counts will make the videos rank more favorably in YouTube searches.
Source: https://www.bleepingcomputer.com/news/security/sites-promoting-free-amazon-gift-cards-dont-deliver-what-you-are-expecting/