Hello,
Almost all the latest routers have adopted the newly designed web GUI, which is more concise and easier to use.
May I know what demands do you need with the firewall settings?
Maybe the new functions in new GUI could meet your need.

I want to do the following:

1. Allow port 53 traffic to OpenDNS server for all clients
2. Block port 53 traffic to everywhere else for all clients
3. Allow ports 25, 80, 100, 143, 465, 587, 993, 995 for specific IP range (DHCP clients)
4. Block all other ports for specific IP range (DHCP clients)

The old TP-Link 9980 can do this, but I had a look at the new GUI for the latest routers and I can't find a configurable firewall anywhere, it looks like it has been removed!

Hello,
Maybe NAT Forwarding under Advanced menu can meet your need.
Here is an FAQ link of how to configure:
http://www.tp-link.com/en/faq-742.html
In addition, the router will block all the ports for the whole local IP range by default except you manually open a port for a specific device.

NAT forwarding cannot meet this requirement. So it appears TP-Link have taken the configurable firewall out of all new routers which is a massive step backwards I don't understand.