OK, so I've now got a working widget in place - I've a "hidden" page with a forum thread list and quick post widget. I can post to the forum within Facebook, but if I click on any of the forum thread tabs e.g. "all recent" or "unanswered" or "unread" etc then the iFrame jumps out of Facebook and into a new window.
I was kind of hoping these tabs would load within the Facebook page not jump out. The widget - "iFrame Embedding" has configurable options e.g. "enable frame embedding" and "redirect to host page" none of which affect the widgets appearing in the Facebook app/tab.
I'm wondering if there's setting somewhere I'm not aware of to configure to stop this working, or would it be a case of maybe copying widgets I want to use and amending them so their behaviour is customise to fit the scenario rather than trying to use something out-of-the-box?