Zoho Desk KB article embedded on another site.

Zoho Desk KB article embedded on another site.

We embed KB articles from Zoho Desk on another site (our application).   When opening the article in a new tab, there is no issue, but if we choose lightbox, we are getting an error 

"To protect your security, help.ourdomain.com will not allow Firefox to display the page if another site has embedded it. To see this page, you need to open it in a new window."

The error seems to point the finger at Zoho Desk - is there a setting somewhere to allow embedding on other domains, or is the culprit someone other than Zoho Desk?   (like CSP rules on a web server, for example)