When creating flash / flex application for facebook, Application Type “Desktop” will work for you just fine, even when your app is deployed. My app is both embedded via iframe in facebook and standalone application (not in facebook). First I tought desktop mode is just to test my app locally and when finished, I should switch to web type. But guess what, after switching to “Web” type, my standalone application refused some actions (upload photos etc.), resulting in error:
error_code: 104 error_msg: Incorrect signature
So, I switched back to “Desktop” and both iframe and standalone applications works fine. 🙂 Correct me if I am wrong, but it seems, desktop application type works for facebook flash / flex api in all cases.