I have previously written about how to predict the next Math.random in Java (and hence Firefox also): http://franklinta.com/2014/08/31/predicting-the-next-math-ra...
The TL;DR; is that it is easy since you only have to brute force around 2^22 possibilities (which runs in < 1 second).
Someone then asked whether it is also possible in Chrome and Node: https://github.com/fta2012/ReplicatedRandom/issues/2. After examining the MWC1616 code I saw the same “two concatenated sub-generators” problem explained in this post. The implication of it is that you can brute force the top and bottom 16 bits independently. So it is also easy since that’s just doing 2^16 possibilities twice! Code: https://gist.github.com/fta2012/57f2c48702ac1e6fe99b