How is Facebook avoiding mixed content (SSL/non-SSL) warnings?

Question

I signed up to Farmville and I get a URL like:

https://apps.facebook.com/onthefarm/index.php?ref=tab

At the bottom of the page are ads which are served not using ssl - they are pulling in regular http calls. How are the mixed content warning dialogues suppressed? Is it trickery or due to frames?

Answer 1

Looking at the code my guess would be frames - since facebook killed off fbml tabs all facebook apps run in an iframe so the content of the frame must be ssl but the rest of the page not.