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.
I'm reading and following along. The current version of Oracle VM VirtualBox Manager(4.3.12 including the Extension Pack) is being used for this follow along on Mac 10.7.5 as well as Mac 10.9.3. I am seeing the same issue in both versions of Mac. Upon following your directions, specifically Figure 2.6i, I had a PCBSD install w/o a network connection. You recommend Bridged, I ended up switching to NAT and when I booted up, I was able to ping bsdnow.tv :D Here are my settings link to screenshot of my Figure 2.6i settings