VCF in web server file

[Rich]

I want to put a Vcard in a web server file so that accessing http://place.com
loads the Vcard contact, and I can have http://place.com in a QR code.
(This is so I can use prettyqr, which must only have a limited amount
of data in the QR to work properly).

I have this almost working, but when I scan the QR and open the
browser, it shows the text of the VCF file rather than opening the
contact (refreshing then downloads the file and opens the contact).
Any suggestions as to if I can change the HTTP headers to make this
work?

(Also, the file is the default for the URL, not a named file - I have
an index.php file that returns the Vcard as a text/x-vcard stream).