There's argument and reasoning in the bug (https://bugzilla.mozilla.org/show_bug.cgi?id=501605 https://bugzilla.mozilla.org/show_bug.cgi?id=501605) and other it

There's argument and reasoning in the bug (https://bugzilla.mozilla.org/show_bug.cgi?id=501605 https://bugzilla.mozilla.org/show_bug.cgi?id=501605) and other items linked to from that discussion. Long story short: some of the Windows versions that libnss runs on are unable to provide as much entropy as libnss's PRNG wants to be seeded with, without resorting to gathering it from places like the tempfiles directory.