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.
For this model, the HPLIP driver is recommended. In PC-BSD®, the HPLIP driver is available as an optional system component called “pcbsd-meta-hplip”. You can see if the driver is installed, and install it if it is not, using AppCafe®. In order to see the driver shown in Figure 8.14c, make sure that the “Raw Packages” box is checked in the “Browser View” menu.