When you start the Firefox web browser, it will attempt to determine if the network connection available to it when it starts is via a captive portal. If you use a hotel's Wi-Fi service, a free WiFi service provided by a restaurant or other business, or some other public WiFi service, when you first open your browser you may see a web page asking you to accede to terms of service, an acceptable use policy, or to provide some authentication information, e.g., perhaps your name and room number for a hotel, or to provide payment information if you are accessing a wireless service that is not free. You won't be able to go elsewhere on the web, at least not easily, until you deal with the demands/conditions specified on the captive portal page.
Firefox makes a determination on whether there is a captive portal
constraint by attempting to download the file success.txt
from
http://detectportal.firefox.com/success.txt (there is only one word in
that file, the word "success". If it can successfully
retrieve that file, it can assume that it is not constrained by a
captive portal. You can see such attempts using the
free and
open-source (FOSS)
Wireshark
packet analyzer
utility by
specifying a filter of "http.request.method == "GET".
If you don't want that check to occur, you can turn it off by typing
about:config in the address field where you would normally
type a URL in Firefox.
You will see a warning page stating "This might void your warranty! Changing
these advanced settings can be harmful to the stability, security, and
performance of this application. You should only continue if you know what
you are doing." Click on the "I accept the risk" button. Then, in the
Search field, type captive. You should see a list of
entries, one of which is network.captive-portal-service.enabled.
The default value is "true".
If you double-click on that entry, you will toggle its value, so it if is "true", double-clicking on it will change it to "false". When it is set to "false", Firefox will no longer perform the captive portal check.
Some IP addresses associated with the fully qualified domain name (FQDN) detectportal.firefox.com are 72.247.8.185 and 23.3.97.88. As you can see from the nslookup query below, Akamai Technologies, which provides cloud computing and content delivery network (CDN) services to other companies and organizations is hosting the portal detection service for Firefox.
$ nslookup $ nslookup > 72.247.8.185 Server: 128.183.10.134 Address: 128.183.10.134#53 Non-authoritative answer: 185.8.247.72.in-addr.arpa name = a72-247-8-185.deploy.akamaitechnologies.com. Authoritative answers can be found from: > 23.3.97.88 Server: 128.183.10.134 Address: 128.183.10.134#53 Non-authoritative answer: 88.97.3.23.in-addr.arpa name = a23-3-97-88.deploy.static.akamaitechnologies.com. Authoritative answers can be found from: > exit $
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