Agree.....but it will also remove any paint from the frame.
If you have any idea what kind of paint was uses, latex or oil based, that might help in choosing a stripper.

Also I would take the sash out and do this outside on a sawhorse or table/bench of some sort where you can lay the sash flat.

Paint thinner probably won't do anything. If the paint on the glass is latex, then denatured alcohol or even rubbing alcohol should soften it enough to make removal easier. If it's oil based paint, then you will need a stripper or lacquer thinner.

Whatever product you use, you need to apply it liberally and leave it on for at least a few minutes to work on the paint. That's why it would be a lot easier to do this with the sash out of the window and lying flat.