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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.
Logitech G devices with the Lightspeed dongle still work with no pairing software (the dongle is pre-paired). You'll need the G software to change things like DPI though.
Ya most of them are good w/o pairing, but if for whatever reason you need to pair then the software has changed.
I use a G603 (wired) and MX Master.