I don’t know why distro maintainers do what they do, but they can use policies or autoconfig to set non-standard default values. It’s commonly used to set the distro homepage as the default page when you open Firefox but I guess some distros take that a bit further.

As you can see from some of the other replies many of us don’t have those config options by default, and according to the Mozilla Knowledge Base these options are not set by default in Firefox: “This preference does not exist by default.”

• kb.mozillazine.org/Network.security.ports.banned
• kb.mozillazine.org/Network.security.ports.banned.…