There is a common misconception about the term "portforwarding" and the confusion is pretty prevalent throughout the online gaming community. Most online games including WoW use a combination of UDP and TCP ports for the gaming client to talk to the WoW servers (let's call it the OUTBOUND direction). The way it works is that the client (let's say user's PC even though Mac is also a client) initiates a connection to WoW server over one of these ports:
So, once a client sends data packets to a WoW server on let's say, TCP port 1119, then the server can send packets back to the user through that same connection. Basically, the PC opens up a conversation (known as a TCP socket), and both client and server can now talk back and forth. You home router/firewall, etc sees that the client talked to the server FIRST and now ALLOWS the server to talk back, but ONLY because the client started the conversation. Even though UDP is a different protocol most home router/firewalls and even university and corporate firewalls treat it the same, meaning, if a client (Pc or Mac) inside the firewall sends packets to a server outside the firewall, then the router/firewall allows the server to communicate back. BECAUSE the client talked first, the router/firewall remembers which of the PCs in the home network started the conversation and then can route the packets from the server back to the client PC.
Where portforwarding comes in to play is when a server needs to talk to a client and the server needs to initiate the conversation (known as the INBOUND direction since we're talking from the perspective of the WoW user). If the home router/firewall has 5 PCs behind it which are all on a private, NAT'd network, then if the PC didn't send the packets first, then those packets that arrive from the server to the firewall/router don't have a clear destination to go to. (i.e. there is no association in the router's memory to know which of the 5 PCs to send the packets to.) So in this case portforwarding would be static rules configured in the home router/firewall to tell the WoW server that if packets come in on this specific TCP or UDP port, then send them to PC #1 ( and not PCs 2 to 5).
However, this isn't necessary for your average WoW user. If it WAS necessary, then it would prevent more than 1 person in a home from playing since the home router could only forward the packets to one PC.
What the WoW client PC REALLY needs to understand is whether those ports above are being BLOCKED by your home firewall/router (or software based firewall on your pc/mac, OR university, corporate, or public hotspot firewall, etc.)
Some router/firewalls will block some or all of those ports I listed above. In the case of coroporate and university firewalls a lot of those entities block all ports (there are 65536 udp and 65535 tcp port) to begin with, and then only ALLOW specific ports for which there is a valid use (and WoW seldom is on this list unless a network admin goes back in to add them.)
For home PCs some firewall software can be very picky and try to block most ports. What you need is a tool that can try to send traffic from your pc/mac out to the Internet on those specific ports to see whether some intervening firewall (yours, or your ISPs, or your university/corporation) is ACTIVELY blocking those ports. If your PC can send packets to a server on the Internet over the needed ports, then it stands to reason it can send packets to the WoW specific servers over those same ports.
Firebind is a site that provides that test. It has a WoW specific test.
In summary, portforward, canyouseeme, yougetsignal, and a bunch of other sites test for portforwarding rules and do the test in the INBOUND direction. But what you really need is a test for blocked ports in the OUTBOUND direction, and only Firebind provides that. I think the reason that the waters have gotten so muddied over the years is that the tests that those INBOUND sites provide are very simply and only represent a few hours of programming work. But the Firebind OUTBOUND test is a lot more complicated to perform but now that it's available it's getting a lot of use in the online gaming community.