I can\'t load facebook into an iframe, in a web page like the following one:
If you use Firebug or Google Chrome's developer console, you can see the following error
Refused to display document because display forbidden by X-Frame-Options.
X-Frame-Options
DENY
The page cannot be displayed in a frame, regardless of the site attempting to do so.SAMEORIGIN
The page can only be displayed in a frame on the same origin as the page itself.
Here is another related stackoverflow question Overcoming “Display forbidden by X-Frame-Options”
Google and Facebook are using a X-Frame-Options in the HTTP response header to avoid the content being loaded in a iFrame.
The X-Frame-Options HTTP response header can be used to indicate whether or not a browser should be allowed to render a page in a or . Sites can use this to avoid clickjacking attacks, by ensuring that their content is not embedded into other sites.
Source: https://developer.mozilla.org/en/The_X-FRAME-OPTIONS_response_header
I don't think it is possible for you to override this setting.