TP-Link (TL-WR1043ND) Router - Can't Access IP From Outside

I've just installed DD-WRT (DD-WRT v24-sp2 build 21676) into my TP-Link (TL-WR1043ND) router. I've setup port forwarding for port 80 to my machine port 80 and it works well under LAN access (checked from my PC and cellphone connected to LAN).

I'm trying to access the testing server from outside through a web proxy, and other sites that check whether my public IP is up, but I can't figure out why I'm unable to access from outside while LAN access is fine.Server is on OS X Mountain Lion with disabled firewall.

I've find it strange to not have an Hairpin NAT issue (I'm able to access the server from LAN through the public WAN address), which is generally a common problem, but still, have this issue.

I've used a web based port scanner and it tells my serving port (9999, not 80) is open (other ports are not), even though I'm unable to browse it.I've learned people can access my server on 9999 port from outside! Now I don't understand why I'm unable to access it with the web proxy tools I've tried.

How can I check, from my machine, that It's serving content correctly, with some online tool or proxy that would access it from outside?