Lucky it's glass so you could try any number of chemicals. I would probably start with a very sharp (new) scraper blade. If that doesn't work, Acetone (nail polish remover) maybe.
Maybe. I suspect the glass has a UV and self cleaning coating of some kind. There's an opportunity here to make the situation worse (further damage) before it gets better (new panel) I think.
Has anyone had any success removing fiberglass resin from things* fibreglass resin should not have been attached to?
* is this case, glass