Sorry for the inconvenience. Known Navigation header breakage, its being "rebuilt."
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.
EasyPBI is a graphical application that makes it easy to build a PBI module from a FreeBSD port. Beginning with PC-BSD® 9.1, EasyPBI ships with PC-BSD® and can be found in the Control Panel.