Sorry for the inconvenience. Known Navigation header breakage, its being "rebuilt" but forward nav should be ok now.
There may be other unforeseen breakage primarily in the handbook portion of the wiki.
The Table Of Contents section of each "PC-BSD® Users Handbook" page may be the best workaround.
If you are using GRUB version 2, run the ls command within grub to determine the names of the disks and partitions that can be seen by GRUB. This will help you determine which drive options to use when setting the root option in the examples shown in Adding PC-BSD® to GRUB Version 2. The output of this command will vary depending upon your disk layout and the naming scheme used by the Linux distro. When you are finished using grub, type quit to leave the utility.