There are five options:
Update 6L: October 2016 firmware plus 13-Feb-2017 ROM, low vector aimed at all models of Pi, see here. Includes Serial and GPIO module in ROM. Has some issues with screen mode changes.
Update 8H: February 2017 firmware plus 6-Mar-2017 ROM, high vector including Serial and GPIO modules, aimed at all models of Pi, see below for contents of zip file. This is the EDID beta ROM and contains an updated screen configure plug-in. The ReadMe file has been updated (25-Mar-2017) to give a longer and clearer explanation of the update process.