Hi Chris,
Normally what happens after you login at facebook is that you come back to the portal with the oauth token from FB. At that stage, Liferay will try to invoke the auto login classes to see if any of them evaluate to true and if any of them do (eg. the Facebook in your case) then it will lookup (or add) the user to Liferay and then auto-log you in. If this is not working there could be a few reasons. First and foremost, can you tell us if you are overriding this properties in your portal-ext.properties file (or derivative if you use include-and-override statements)
auto.login.hooks
also, can you provide the settings that you are using for your facebook auth?
