Great improvement on allowing private browsing to be opened in a new window (like Chrome), but terrible decision on having all new private windows use the same session (like Chrome). I'm a web developer and sometimes I need to log into multiple accounts on the same website (like GoDaddy or Yahoo) or test various websites under different conditions, and separate sessions for each private window would be great.

Frankly I don't see why each new private window I create should share the same session; this never made sense in Chrome, and it seems like having this ability would put Firefox a step ahead of Chrome. I can see why you'd want the same session for links you click that open new windows or popups, but if I make the direct action of opening a "New Private Window", you'd think it would its own private session too.