Why is Firefox establishing connections to detectportal.firefox.com on start?

[harlan4096]

When you monitor the network traffic of the Firefox web browser you may notice that the browser establishes a connection to detectportal.firefox.com on start by default.

The connection is one of the first that the browser makes automatically and you may wonder why it is being made in first place.

The name provides a clue; Firefox attempts to find out if the Internet connection is limited. Hotels and other places that provide access to the Internet make use of captive portals that limit connectivity unless the user enters a code first.

Web browsers and any other Internet software cannot establish connections when that happens since every attempt is blocked by default; this means that the browser cannot check for updates or load sites that are not in the cache.

Firefox tries to detect if a portal is active with the help of that initial connection. If that is the case, network connections are held back as they would not be successful anyway.

Firefox users who use the browser at home or any other location that is not making use of captive portals for Internet connectivity, can block the connection attempt as there is no downside to doing so.

Note: A user mentioned in the comment section below that disabling the check impacts Firefox's new Private Network ability to connect.
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