Every once in a while, we need to go to a website that has a non-standard port. For example, the address might look like this: https://localhost:888 (This would be for the 3ware management interface for example).
In Mozilla Firefox, you’ll get a screen that looks like this:
Obviously, this can be a real pain in the butt. There is a way around it though. The secret is not well documented, but all you need to do is open up firefox and in the address bar (Where you would type in https://www.yoursite.com:888), you would type in the following without the quotes: “about:config”
A page full of variables is going to show up. Right click in this page full of variables and select create a new string. A box will pop-up and inside the box field, create a string called (again, without the quotes) “network.security.ports.banned.override”. Give it the string value of: 1-65535 and then hit ok.
You will now never be bothered with that message again. Hope it helps.