Here is a quick guide on how to remove Firefox's error message when trying to access resources on restricted ports, such as port 87:
This address is restricted
This address uses a network port which is normally used for purposes other than Web browsing. Firefox has canceled the request for your protection.
1 Open Firefox's settings: about:config
Open Firefox's preferences by typing the following URL in Firefox:
2 Find the settings network.security.ports.banned.override
In the Filter box, type in
3 Create if not found
If you can't find such a preference, right click to open up the pop-up menu and pick New and then String.
As preference name type
network.security.ports.banned.override and 87 as the value.
Afterwards it should look something like this:
4 Modify if exists, and how to add multiple ports
If such a preference already exists, you can specify multiple ports. Either as a range such as 1-1024 or even combine with a comma separated list such as 87, 150-300, 350, 400, 450-500.
5 Refresh the page
Just refresh the page and you should have no problems accessing the resource.