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.
PC-BSD® is a community project and relies on involvement from its users and supporters. This section lists some ideas for becoming involved. We also have a list of Tasks Looking for People if you are looking for a specific task to assist with.