Some background:<p>Facebook made a change to allow the use of iFrames in Facebook Page tabs. The development roadmap stated that no new FBML apps would be allowed by the 11th of March and Facebook encouraged developers to create iFrame applications even before that.<p>There is a critical bug that prevents iFrame applications from being loaded in Facebook Page tabs for users that are using HTTPS on Facebook. Since Facebook is encouraging users to use HTTPS for security, this is impacting developers that followed Facebook's recommendations.<p>To fellow developers out there, be careful. Wait for a while before jumping onto the iFrame bandwagon.