Regarding problem logging on to the router. I have an AC3100; same problem. I have tried multiple permutations of the IP address and logon.
After reading the post above, I tried it with the :8443. Firefox blocked the access because it was self signed. It popped up a message. You can add an exception. That may be your problem. Though you should see the message.
After reading the post above, I tried it with the :8443. Firefox blocked the access because it was self signed. It popped up a message. You can add an exception. That may be your problem. Though you should see the message.