The issue is that if you do not set permissions in the manifest, clicking allow in the safari UI would only return a blank URI, "". The original extension in this case would also just return an error.
I've modified the manifest so that it is asking Safari for wider permissions, so that when the permission is granted by the user, the proper URL is returned.
I've modified the manifest so that it is asking Safari for wider permissions, so that when the permission is granted by the user, the proper URL is returned.