Things will break. We shall track the breakage.

I don't know what the procedure is for handling this, or even if it is relevant be adding broken extensions before this code is even finalised. However, I am having trouble getting anyone to take seriously the implications of per-window private browsing on cookie management. Until the cookie management functions get a way to work with the private browsing cookie database (eg. bug 823941), and things like cookie-changed notifications are similarly modified (eg. bug 837091), this featured addon at least is totally broken and cannot be fixed: https://addons.mozilla.org/en-US/firefox/addon/cookie-controller/

Tracker with all dependencies closed.