Link to the userscript: https://pastebin.com/t4BAfxfm. This is a scam where the victim is tricked into believing they can get free Steam gift cards or other types of gift cards by running a script in their web browser. It claims that when running the script it will trigger an expired payment session and that the website will both deliver the key and return the Bitcoin to the user. It also claims that it is important to order something over 40 USD for the script to work. The truth is this userscript in javascript running in Tampermonkey actually replaces the Bitcoin address with that of the scammer on the website and the victim sends the Bitcoin to this address. Then the website support system gets overloaded with people who are convinced that they paid for their key and didnt receive it so this has extra side effects and can increase the chance that merchants will drop accepting cryptocurrency because of support spam. Every time the merchant changes the code in checkout the scammer changes his code as well and release a new version in an endless loop.