I gave up waiting for an answer from the Ford Forum and finally went to the local Ford dealer's Service Department. The Service Manager referred me to his Body & Paint shop. A worker there tried to use a small screwdriver to loosen the clip which holds the mirror in place. Failing that, he referred me to a local glass shop which does their windshield replacements. Upon arriving there I was told that a special tool is required, which is owned by yet
another local glass shop. I'm going
there tomorrow morning. These things shouldn't be this difficult