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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.
You don't need to use anything web to set up your Logitech devices. You only need web if you want to sync your settings between multiple PCs. It's a very handy feature, by the way. Your hate is misguided here.
If this is just for syncing settings, why does it use WebUSB? Why use a browser at all for that?
To push settings directly to your dongle.