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.
This happens on Windows, right? What would happen on Linux, would the keyboard still work as it gets connected?
Yes. They are using WebUSB. That's only supported on chrome browsers for now. But it also works on Linux. The home automation community makes great use of that api.