Since my husband is a painter, I have learned a lot. There are these flat edge razor blade scrapers/knives (Home Depot carries them for under $3). They are great for getting sticky/hard things off of glass, smooth floors, etc. We spray the area first with 409, after it sits for a minute, use the razor knife to gently scrape it off. I have used mine to clean many windows of years of dirt and grime, take paint splatters off, etc.
By April R. from Pilot Point, TX