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As if it wasn't bad enough that they want me to use a random internet service to add a keyboard to a usb wifi receiver, they have the balls to put this for Firefox users. I clicked out of pure curiosity, as I'm not even remotely interested in involving a corporate internet service in getting my keyboard connected to my computer. This is the message you get now on Logi Options software if you have a Unifying Receiver: 
For the curious: https://logiwebconnect.com
EDIT: some people on the thread have brought up that the error message being displayed for Firefox users is due to the WebUSB API not being implemented by Firefox due to security concerns. This still does not justify having to use a web app to plug peripherals to a PC.
I didn't even know you could pair other devices to a receiver. Is this only for newer receivers, or can old ones be re-paired or pair multiple devices?
It's been a thing for quite a while so there's a good chance whatever kit you have supports it
Watch out for Old Unifying Receiver and the newer Bolt Receivers ! Mutually Exclusive devices/receivers!!! This is why I have stopped buying newer Logitech devices. Looking for some other peripherals company that treats and makes better products for their valuable customers!