turn off interactivity on the container on the layout?
Usually progressive downloading is very desirable. What problem are you trying to solve by not using progressive downloading?
The problem here is (for reasons too stupid to get into) buying a custom certificate is not an option, and apparently FMS won't use the built-in SSL certificate to secure progressive downloads. So I would rather disable progressive downloads than have them take place "in the clear". If that's not possible I don't really know what to do. Stay with 13 for Server, I suppose?
FMS13 can't use SSL for progressive download, so the check box is in the SSL setting. If you use SSL, it appear for confirming use progressive download without SSL.
FMS14 can use SSL for it, so the checkbox is always there.
It may be UI change, not configuration.