To enable Facebook comments, start by clicking on the cog icon on the right side of the site header bar, and select Settings.
Next, you will need to obtain a Facebook Application ID by following the instructions bellow:
1. Go to: http://developers.facebook.com/apps, sign into your Facebook account and click on "Register as a Developer".
2. Fill in the short questionnaire et voila you are a developer.
3. Next, click on "Create New App" and fill in the pop up box and click "Continue.
4. Another window will pop up. Copy the App ID at the top of the scene.
5. Select the "Comments" section in the left sidebar and select "Facebook Comments" as your comment engine. Enter your Facebook Application ID into the field titled "Application ID" and click "Save".
If you would like to disable Facebook comments then select either "Built-in-comments" or "Disable comments" and click "Save".