Pre-Master Key (PRG) (Firefox)

As known, during the ClientKeyExchange phase of the Handshake of TLS, the
client generates a 48-byte random number called premaster secret using a
Pseudo Random Generator which is used to calculate the master key and the
key sessions.

 I would like to know which Pseudo Random Generator functions are used to
compute and produce the pre-master Secret which are used in TLS1.2 in
firefox.
Thank you very much in advance.