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.
This category can help to identify pages with NavHeader and consequently ought to be part of the current handbook on the wiki.
This category currently contains no pages or media.