On desktop, this is fantastic. With mobile traffic becoming the majority web population, making reftagger responsive friendly would be a good move. I'm just thinking out loud here.
Currently, touch interaction can be confusing for users. When tapped, a link opens but can easily be accidentally tapped again or if the popup is closed and the user taps it again he is redirected. That's the biggest one really. Rather than using a focus affect with js, a visible close button would be helpful for responsive layouts.
I'm not finding a responsive site to see a demo of the styling, but the popup would need to respect the max screen size so nothing appears off screen.