I have had my Kindle Fire HD connected to my computer dragging and dropping files on and off of it. And at the same time There also was a book open and viewable on the Fire.
It was like the kindle was two machines, one connected to the computer for file transfer and another that acted just like nothing special going on and you could read a book. Tho I can not see the utility of it.
Not at all like the K3 where it was ether mounted or unmounted to the computer. The fire can be both it seems.