I used to work in a tint shop and we used amonia mixed with a little water in squirt bottle. and a razor blade and a sponge. Let it sit in the sun for a little while and it will be easier to remover the glue.
Well I used straight acetone, and it ate the glue off the window. It worked real well, took me about 10 minutes to do the whole driver side window. And I got the acetone for it for free from a lady at Advance Auto Parts that I flirted with. So it took me 10 minutes of my time, and no money to do.