i was looking into why dl.securecusercontent.com urls give SSL error. It seems the domain doesnt have a proper SSL certificate. This is an article i found and the link below is from that article. These are links generated on OSX from the right click or context menuhttps://dl.dropboxusercontent.com/s/hriinb9w3a2107m/iPad%20intro.pdf
@Rombout V. I've split your message off to its own thread, as the original thread was actually about a different host ('content.dropboxapi.com') than what you're referring to ('dl.dropboxusercontent.com').
Also, note than in your message you actually referenced something else, "dl.securecusercontent.com", which is not a Dropbox host, but that was presumably just a typo.
Anyway, dl.dropboxusercontent.com appears to be being served with a valid certificate from what I can see, e.g., as seen in Chrome:
Can you let me know where you're seeing an error and share the full error/output you're getting?