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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.
Well, no, this is using the WebUSB most likely which is not supported by Firefox. Regardless of the security implications of the WebUSB API, this is a Firefox specific issue
I thought that you have to open a website to connect some peripheral was the issue here. You should not need a browser for that at all. The issue here is very clearly Logitech.
Well this is true only in the sense that, half the available browser engines don't support it.
72% of users use a browser that supports this API. They're probably all Chromium-based browsers though. https://caniuse.com/mdn-api_usb