Setting the Canvas Size parameter for the Resizable Iframe alone does not allow you to automatically resize the canvas to fit your content. There are a few more things you need to do. Check out the Resizable IFrame page for complete instructions.
You basically need to create an HTML page known as a "cross-domain listener" (this is as simple as copying and pasting their sample file), and then copy the Javascript code snippet at the bottom of all your application pages, Javascript will do an iframe resize after loading the content.
The wiki page has improved since its last use, so hopefully it's pretty simple. If you have problems with its operation, make sure that you verify that you have correctly edited the javascript fragment to point to your cross-domain recipient page.
Jan 2011 update . Some comments are coming in, so I decided to update. I believe this answer is still more or less correct, although the documentation has changed. Facebook has moved away from FBML and updated its Javascript SDK. The current method for loading the Javascript SDK is on the main page of the Javascript SDK , and below are the methods you can use to resize canvas, FB.Canvas.setAutoResize () and FB.Canvas. SetSize () . You still need to set your canvas as changeable in the application settings. It looks like they replaced the need for a cross-domain file with a new SDK, but I haven't tested it myself yet.
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