Steps to reproduce:
1. Create new Site Page (Layout) with Type=URL and link it to Document Library File Entry (e.g MS Word document)
2. Try to download document using Friendly URL of this page
Server responds the following headers:
Content-Disposition: attachment; filename="filename.doc"
It allows us to download file, but browser cannot recognize that it is a MS Word document.
When downloading documents by direct link (/documents/.../.../filename.doc/d2659df7-d3bf-43...) everything is ok (Content-Type: application/msword is sent).
I believe it can be easily fixed as we can get information about the file (Content-Disposition: ... "filename.doc").