Heads up, page admins! As of October 1st, Facebook announced that any iFrame page tabs not hosted on a secure server under HTTPS will not be displayed to users browsing under HTTPS. This article will tell you what you need to do.
According to Facebook's Cat Lee, "The content will not be accessible for users with secure browsing turned on. There will be a page that states something close to: This app does not support secure browsing."
To help page admins