To install GRUB as your boot-loader, use the following command:

# grub-install /dev/ada0 (replace ada0 with your disk)
# grub-mkconfig -o /boot/grub/grub.cfg

This version of GRUB can be used traditionally or with
PC-BSD style boot environments.

Additionally, when using GPT, you must have a created a
"bios-boot" partition at install time. This partition is used
for GRUB's modules for GELI/ZFS and related bits.

Traditional Setup
--

When the "beadm" utility is not present, grub-mkconfig
will use the standard GRUB detection scripts for setting
up your /boot/grub/grub.cfg file.


Boot Environment Setup
--

If the "beadm" command is installed on the system,
grub-mkconfig will use it to setup /boot/grub/grub.cfg

For it to properly detect / populate your BE menus you
must have your root zpool setup in the following manner:

<tank>/ROOT/<be>

Where <tank> is your zpool, and <be> is your '/' mountpoint.
The "beadm" utility must be installed and working before using
GRUB utilities.