Was trying to access some ports on ours development website which someone mapped it to 6000.
Port 6000 is used for X11 protocol ( and 79 is used for finger).
Internet Explorer works fine but Google Chrome and Firefox don´t.
For Firefox exists one solution

Solution:Unblocking/allowing ports in Firefox

Launch Firefox

Go to the address bar and type about:config. Firefox will complain about some warranty just click ok or “I’ll be careful, i promise” button

You will see the list of configuration.
Anywhere inside the list of configurations, right click and say New –> String

In the string value, enter network.security.ports.banned.override then click OK

It will now ask you what port, say 6000 (in my case) or whatever port you need to have firefox access. Click OK.

And try again to the website you want to access. These settings should remain forever.

For Chrome, we’ve got some bad news, it is not possible to access certain ports.

See Chrome banned ports here: http://src.chromium.org/viewvc/chrome/trunk/src/net/base/net_util.cc
(look under the kRestrictedPorts directive.)

Original post from http://highsecurity.blogspot.com/2009/07/google-chrome-and-mozilla-firefox-non.html
(my post is a copy with a few changes only, all rigths for the author)