I am using "facebook, comments widget" on my site
and wondering, how can I review comments before they get published?
that's simple. Add the tags <meta property="fb:app_id" content="YOUR_APP_ID"> and <meta property="fb:admins" content="your_profile_id"/> if you haven't done so already, together with the other tags. If everything is right, the same comment box will have a "Settings" link on top. Click that, and select "let me approve each comment before it appears". There are many threads if you search. One discussion is here Facebook comment moderation tool