What are the /firmware and /efs partitions on Samsung devices
According to this linky here this is what it has to say


  What is EFS? It is a place that stores your Android smartphone
  important data like Wi-Fi, Bluetooth MAC address and IMEI
  (nv_data.bin).


After reading the above linky, it would be prudent to make a backup of that partition otherwise well and truly hosed! :)

As for /firmware I am guessing that is where the original stock firmware goes into when updating via the official route a lá Kies. 

If anyone has a better insight feel free to comment, and I will gladly amend this accordingly :)