It literally is their job. One of Mozilla's roles is to give their opinion on proposed web standards. It's one of the factors that determines what actually becomes a standard. WebUSB is Chrome (and derivatives) only at the moment. You can not like where they landed, perfectly valid, but they were asked.
Yes, but instead of saying "this spec is shit and full of vulnerabilities. Let's work on improving it", they just refused to participate in the discussion. What a childish POV.
I don't think that's a fair summary of Mozillas Position on the WebBluetooth/WebSerial/WebUSB specs. Interacting with arbitary devices has arbitrary consequences, mozilla seems to assume users are not able to understand these consequences and therefore cannot consent to it.
