You don't show what body_popUp is set to but, assuming it's valid HTML and it's placed in the extension,js file, the code look fine.
In general, note that the notification is smart and only appears when it detects user movement in the browser. This algorithm is used as a way to ensure that the notification is seen, as it assumes the user is looking when activity is detected.
[Disclosure: I am a Crossrider employee]