Sorry to hear about this problem. The installer (or Firefox) has discovered a setting file pointing to a profile folder, but that folder either no longer exists or there is a Windows permission problem accessing the contents of the folder.

Are you trying to reinstall Firefox and connect to existing Firefox data, or are you trying to get a clean start?

You also could look at this article: Firefox ausführen, wenn Ihr Profil fehlt oder unzugänglich ist.