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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 generally don't need to download the software to use the stuff and Logitech has been OK about that. The dongles are paired out of the box and bluetooth just works, but if there are problems (or button mapping) then the software is needed. Eg. some of them will pop up an installer when you plug in the device (I know my Razer keyboard has some shite software that boots at login.