Yes, I've read many, many stickies on fixes for this.
But I am still behind a firewall.
UPnP is enabled.
My Windows Firewall is disabled, completely.
Ports are forwarded, and working.
But I am STILL, behind a firewall..

Any help?

You either operate in UPnP mode or Port Forward mode for a specific program, not both. I can at least ascertain you are using Windows.

Checked my router settings again, "UPnP is enabled", pretty sure it cannot be that?
I'll mess around with the settings, see what i can do, i guess

I just opened port 6436 (used PortChecker to make sure it was opened), selected the manual port option in Limewire, but still, saying behind a firewall.

Running with no software firewall isn't a good idea. You can turn Win firewall on (providing you're not using any other software firewall) & allow FW through the firewall.

If UPnP is enabled in your router, you can try ticking the 'Use UPnP' box within FW's tools > options > advanced > firewall. Click Apply > ok to save the change.
Some routers aren't reliable in UPnP mode so in that case you could look at port forwarding.

Did you first of all set up a static IP address & then set up port forwarding within your router's config?
If we had your system details then we'd know your router brand & model & could give you port forwarding instructions specific to your router.

I'm sure that you saw this amongst all the stickies & forum rules: System details - help us to help you -> Provide these details when you post!!!

Could you please post back with answers to those questions?