Some background: on Unix, Firefox obtains seed entropy from /dev/urandom, while on Windows it calls RtlGenRandom() for some reason instead of CryptGenRandom().

Some background: on Unix, Firefox obtains seed entropy from /dev/urandom, while on Windows it calls RtlGenRandom() for some reason instead of CryptGenRandom(). This seeding material is then fed to the random number generator, a NIST SP800-90 Hash_DRBG. However they do obtain additional (optional) entropy (if you're familiar with the NIST DRBG's, then I'm talking about the 'Additional Input' parameter) by reading system time while periodically reading a bunch of system dirs to advance time in a non-deterministic manner. And that's where this bug creeps up.