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.
It doesn’t. Logitech does provide software for doing this. No browser needed. https://support.logi.com/hc/en-us/articles/360025297913-Logitech-Unifying-Software
You’re right, the site rendered weirdly so I had trouble finding the arrow to select my OS at first, but it does provide a proper driver for this! The thing OP lists seems to be the default, which is LUC-for-Chrome.