there's a beta feature called "Reference Previews". didn't see it here, but ATM, it exists in beta preferences on enwiki and hewiki, and probably most wikimedia wikis.
presumably not a "gadget", but part of core.
these two features "collide" - both show the cite note in two separate popups.
one of them should check if the other is on and disable itself. i think this one already self-disable when the old "popup" enwiki gadget is on, and something similar should be done WRT the beta feature too.
peace.