Apple has released EFI Firmware Update 1.5 for the Mac Pro. The update is recommended for all Mac Pro (Mid 2010) models and addresses an issue that prevented the firmware password prompt from being displayed as well as another issue that prevented the Boot Picker from being presented if Ethernet is connected to a network without DHCP.
The update requires Mac OS X 10.6.4 and is a 1.96MB download via Software Update. It is also available for download here. You can read Apple's knowledge base article about the EFI firmware updates here.