It is enough for you to only once have used the same browser / profile with both accounts. There are cookies to keep track of who is who and then it is a matter

It is enough for you to only once have used the same browser / profile with both accounts. There are cookies to keep track of who is who and then it is a matter of matching identifiers on one platform to the other. It is hard to believe you have been diligent enough to keep things absolutely 100% separate between Facebook and amazon.