I tried fingernail polish remover and it worked super easy and fast.
This is a page about removing masking tape from windows. Masking tape that is left too long on windows can be difficult to remove.
Attach Sink Skirt with Clear Tape
Cornstarch and Vinegar Window Cleaner Recipe
Removing Labels from New Windows?
Removing Masking Tape From Tinted Windows?
Faux Stained Glass Windows
Removing Masking Tape from Windows