From Facebook Developer Wiki

not really any way to file problems....

Please use bugzilla. Thanks, Pete (563683308 11:57, 26 May 2009 (PDT))

e.g.

how do I file this problem ?

Error while processing response There was an error while processing the OpenID response.

No matching endpoint found after discovering http://john.jones.name/

this works fine in other providers I don't understand why facebook fails...

Hi John, Facebook fails because it only supports OpenID 2.0 compliant identities. In your case you do not provide XRDS discovery nor OpenID 2.0 HTML discovery. As you are a Wordpress user, install/update both the wp-openid and xrds-simple Wordpress plugins and then re-setup your delegation. You should be fine then.

Suggestion #1: Ensure that the FAQ has a "How do I use OpenID with Facebook?" and a relevant answer. These things don't spread by word of mouth well when people can't figure it out on their own.

Suggestion #2: Have some way to login directly to Facebook with OpenID for the first time. ( Maybe add a button to the logon page ? )