Sorry to bring up this old topic again, but I would like to say that dealing with old window tinting can be tricky. Instead of using ammonia and a razor blade, you can use a steam cleaner or heat gun to gently heat the tint. This will help loosen it without causing harm. Another option is a spray tint remover or an adhesive remover specifically designed for this purpose. A few months ago, this was the way I removed my tint and started using the sunblinds I ordered from
snapshades.com, as they are more convenient for me. Just remember to follow the instructions carefully. Patience and the right tools will help you remove the old tint without any problems.