I tried heating the glass with a hair dryer and using a razor blade to remove the mirror mounting pad with no luck.
So do I need to get a heat gun or is there better way?

Thanks for you input.
-Don

I just had speedy auto glass out today to put in my windshield and they needed to take off a broken rear view mirror on the windshield. The guy used a small propane torch and gentley heated it up and let it sit for a couple minutes before working at it with a pair of plyers took him a bit as he didn't want to heat it up too quick but it came off just fine.

Nail polish remover/acetone works great. Put a little on a cloth and hold it against the adhesive for a minute or two. Should wipe or scrape off easily.

Thanks for the information. Just to clarify, I need to take off the mirror base, which is glued to the windshield not just the adhesive

use a q-tip and swab gasoline on the top edge and let it seep it. use an old plastic credit card to apply leverage and push from all four sides of the mount. better if you have the plastic pry tools from harbor freight to use as a chisel to push in on the adhesive pad.

Use piano wire or heavy fishing line and slide between the windshield glass and the rubber adhesive. Slide it through like cheese

Heat gun. You want to break down the adhesive. Search out the failure point for mirror adhesive. You may have to heat it several times before trying to force it. I had a parts car that had a big chunk glass out of the windshield where the mirror was mounted. Kind of strange. No cracks just a big chip of glass missing.