How to use picture-in-picture for amazon instant video? On Youtube in safari, you can right click twice to get the PIP option.

However, I can't figure it out for amazon instant video
I don't have access to Amazon Video, so I can't test this, but try out PiPifier (Mac App Store link). It installs a Safari extension that takes any HTML 5 video and puts it in a PiP window. You can read more about PiPifier on GitHub.