Most problems related to Font Book come from using it before knowing how its default preferences are set. Common problems include disabling important fonts, moving them from System to somewhere else, resolving duplicate fonts incorrectly, etc.
I recommend everyone read the PDF file Fonts in Mac OS X before
using Font Book.
I also recommend you review Using and Managing Fonts in Mac OS X
You can undo almost everything done by using Font Book -- except
restoring fonts you have Removed or putting fonts you moved back where they belong -- using the following procedure.
Please read this entire procedure in full before using it. Perform the following steps in the order specified:
(1) Quit Font Book and all other open applications.
(2) Open your Home > Library > Preferences folder and trash the following files:
The first is the preferences file for Font Book. The second is the list of fonts you disabled in Font Book: when you log in, the fonts listed therein are prevented from loading. After deleting the second file (com.apple.ATS.plist) and logging out/in all
previously-disabled fonts will load. If you've installed hundreds or thousands of fonts, this could result in very slow performance when all previously-disabled fonts are loaded.
(3) Open the Macintosh HD ]Library > Caches > ATS folder. If you are the first user defined on your Mac, there should be a folder in there called 501. Trash it. If you are the second user, 502 would be your folder: trash it. etc. If you use Fast User Switching, there may be several 501.xxx, 502.xxx folders with the ATS folder that you need to trash. If requested to authenticate, provide your Admin password.
(4) Restart your Mac.
(5) Empty the Trash.
: In lieu of step (3) you could try:
(a) Font Cache Cleaner
(b) a full System-level cache cleaning with Cocktail
or Panther Cache Cleaner (PCC)
. That would also require a restart. Do not empty the Trash before restarting.
I do not recommend using Font Book in conjunction with other third-party font-management applications.