The website wants to access the key, to prove you are authorized to use the site. That is what the key is for - to access that site.
but in the interface it says
""ask when a site wants too access usb devices.""
not ""ask when a website ask for a key to access the website""
it clearly can access a physical usb device, the key offcourse also could be given on an usb copied too the hd and then uploaded from an hd.