In one of my projects the contao website gets loaded in an iFrame on another website. However in IE7 the cookies of the contao website are treated as a third party cookie.

I used the following fix:
On system/initialize add at the start the following code
Code:
header('P3P: CP="CAO PSA OUR"');
See also http://james.jamesandkristin.net/2005/1 ... t-explorer