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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.
I kind of see the point in this.
Things I can do with Chrome'ish browsers:
All this with a single browser, no 3rd party applications. I think it's called WebSerial and it's a neat feature. Quite sad that Firefox doesn't have it.
If you can really overwrite your operating system with your web browser, that sounds like a security nightmare.
There are multiple steps in between for installations, but yeah the attack surface is quite large…
You have to manually allow bootloader unlocking from within your phone's developer menu which is hidden by default, and then you need to boot your phone into the bootloader menu. Only then will the browser be allowed to interact with the phone, and even then you get messages on the phone that you have to confirm to allow anything to happen.
Nobody's accidentally going to replace the OS on their phone by visiting a website.
It's a protocol/interface for writing to USB. So whatever you can do over the USB cable with software, you can do from the browser.