Additionally, as per RFC1378, non-standard schemes should either be registered with IANA, or should start with x-. If Facebook was being a good citizen, they'd

Additionally, as per RFC1378, non-standard schemes should either be registered with IANA, or should start with x-. If Facebook was being a good citizen, they'd register 'fb' (they haven't), or better yet, use 'facebook' or 'x-facebook'. Also, we don't need a fancy database -- existing vendor's web sites are perfectly capable of sniffing the browser and redirecting to a native app, if it's available -- this is what iTunes does.