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.
PC-BSD® Users Handbook/9.2
The revision #50798 of the page named "PC-BSD® Users Handbook/9.2/en" does not exist.
This is usually caused by following an outdated history link to a page that has been deleted. Details can be found in the deletion log.