Explorer blocking your Facebook app cookies?

You worked hard. Your application works like a charm, the concept rocks, the graphics are great, the client is happy. Still, you know there is one more thing to do: test with the dreaded Internet Explorer.

In your case, the app is a standard Facebook iframe application. You went to great lengths to make sure it stays compatible with IE (that means modern CSS/HTML techniques are off limits). Tough luck, you have to try harder my friend. You see, the application does not work at all! With no error message whatsoever.

Oh, wait a minute, there is a stupid eye icon in the status bar. Once you click it you realize that IE is actually blocking Facebook's authentication cookie! In the default security setting, no less. You are royally screwed.

To make a long story short, here is a 'voodoo' solution, offered by a mastermind friend:

response.setHeader(
  "P3P",
  "CP='IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT'",
);

For the hairy details, get educated by the pros. Groovy!