Regular glue or epoxy won't work. It needs to be a conductive epoxy.
The defroster tab fell off of the wife's Liberty last fall. I went to the local Napa and they have a "LOCTITE Defroster Tab Repair Kit." It was easy to use. Be sure you have some isopropyl alcohol or some kind of degreaser to clean the tab and mounting surface.
It has held so far. The defroster is on a lift window, so it gets tugged on every time she opens the back hatch.
I'm sure that O'Reilly's, AutoZone, etc... have kits also.
Good Luck,
jc