TBB should disable "New Private Window" menu option if disk history is disabled
Because we use browser.privatebrowsing.autostart as defense in depth against disk leaks, "New Private Window" is equivalent to "New Window". This can be confusing to users who will expect their "New Private Windows" to be isolated from their normal TBB state, especially since the UI hints are different for these windows.
We should probably patch Firefox to hide this menu option if browser.privatebrowsing.autostart is set. This seems like something Mozilla should be interested in picking up.