What is an emulsifying material/product that will remove the sticky remaining adhesive from the inside of rear window - without damaging the electronic rear window defogger?

Had a school sticker back there for over 10 years, and now having to remove and deal with the residue, afraid using a razor blade will harm the electronic matting on the inside of the window.

Car is a 99 Mercedes-Benz E300.

Appreciate any helpul tips here!