You may dislike GNOME's Hotspot Login feature that shows a window everytime you connected to wifi hotspot. It is a window that does a certain connection to the internet to trigger the hotspot login page (captive portal) for you. You may dislike it in case you have permanently logged in (seamless) or it takes from you some amount of data downloaded each time it runs. Here's an example of a working Hotspot Login window:
To disable it, go to System Settings > Privacy > Network Connectivity Checking > turn it OFF > close. Next time you find a wifi hotspot you won't see the Hotspot Login anymore.
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