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.
Beginning with PC‑BSD® version 8.2, a PDF of the Users Handbook matching the released version is included as an icon on the PC‑BSD® desktop. In addition, the Users Handbook is published in various formats as listed below. If you are interested in translating a released version of the documentation, refer to these instructions.