This is not just an isolated incident, it's the whole trend of limiting capabilities in the name of security and that's what I was referring to.
However in this particular case, even the security argument doesn't hold, either I:
a) know that I want to use USB - in that case I'll switch browsers or download a native binary (even more unsafe), it's not that I'd decide that I no longer want to flash my smartphone
b) I don't understand what's happening but I follow arbitrary instructions anyway - WebUSB changes nothing.
A native binary can be verified by anti malware systems, and once installed and working, poses no security risk.
A 0day in a browser for the WebUSB system would allow any website to mess with arbitrary USB devices connected to your computer.
While the browser sandbox is generally safe, it is also a huge target, and with a security risk like that, it wouldn't surprise me if it's a prime target for black hats.
I’d be ok with an about:config switch, but given that many people will install anything, paste arbitrary text into terminals, and share their password/pin code with complete strangers for almost no reason, I think we need to stop making our tools less powerful in pursuit of an impossible goal.