On the EX series, the firmware is a distinct download. It is installed via the typical "request system software add" command used to install JunOS. The version I show as the most current (without the issue described in the KB at https://kb.juniper.net/InfoCenter/index?page=content&id=TSB16227&smlogin=true&actp=search )for the EX4200 is 1.1.6 dated July 5, 2012:
> show chassis firmware
Part Type Version
FPC 0 uboot U-Boot 1.1.6 (Jul 5 2012 - 11:58:22) 1.0.0
loader FreeBSD/PowerPC U-Boot bootstrap loader 2.4
FPC 1 uboot U-Boot 1.1.6 (Jul 5 2012 - 11:58:22) 1.0.0
loader FreeBSD/PowerPC U-Boot bootstrap loader 2.4
FPC 2 uboot U-Boot 1.1.6 (Jul 5 2012 - 11:58:22) 1.0.0
loader FreeBSD/PowerPC U-Boot bootstrap loader 2.4