I was searching these forums to find out how to delete some redundant port forwarding rules created by UPnP. The general consensus seems to be that a factory reset is necessary although it was suggested that some browsers might manage it, I could not find any listed.
If anyone's interested, I've found a browser that will delete these rules. It still shows a "no entry" sign when you hover over the red X, but if you click it regardless, Opera Version 12.17 will delete the little devils and although ancient, it's still available to download.
UPnP doesn't create port forwarding rules, it just opens and closes the ports as necessary.
I found out how to do this:
1) Click on "Show IP Address".
2) Press Tab (on keyboard) three times,
3) Press Return (on keyboard),
4) Confirm deletion of the rule.