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.
Translations:What's New Since 9.1/2/en
The following features have been added since PC-BSD® 9.1 was released on December 18, 2012. Users who wish to test or take advantage of these features can either install or upgrade to a rolling release. Once the upcoming 9.2 release cycle begins, these features will be incorporated into that version of PC-BSD®.