I believe that "disabled for your protection and security" is pretty clear, but it does raise the question "but why?". There should be a link to http://www.mozilla.org/projects/netlib/PortBanning.html , so that the user can at least understand why the port's blocked, and how to override it if needed, etc. Something like "For more info, see http://www.mozilla.org/projects/netlib/PortBanning.html"

If Firefox includes a link to that page, will that page have to be localized?

This is what I suggest we use. Just add a paragraph with "For more info, see [link here]". Screenshot of this coming. I don't see why it'd have to be localized, except as a failsafe to the rare event mozilla servers go down, but that's highly unlikely, and I doubt too many people run into this problem to begin with.

There is ongoing discussion about the various error message strings in bug 301208. Tonglebeak, can you check the latest patch there to see if it makes things any better, or if you'd still want that link. FWIW, I don't think we want these pages to link to external sites unless we feel that the average user would be helped by doing so. This sounds more like the type of thing we want to make sure is covered in the help documentation. *** This bug has been marked as a duplicate of 301208 ***