In the View menu select Toolbars, and then Customize to open the customize toolbar dialog. With the customize toolbar dialog displayed, there should be an icon with the label "Bookmarks Toolbar Items" on the bookmarks toolbar. If it is not there, drag and drop the icon called Bookmarks from the customize toolbar dialog onto the bookmarks toolbar. There will be 2 icons called Bookmarks, the one you want will have an icon that looks like a sheet of paper (it does on Windows, I believe it is the same on the Mac).

You may also need to check http://kb.mozillazine.org/Corrupt_localstore.rdf

You the man! Your suggestion solved the problem I encountered. First time in years of using Firefox that this happened. Reason still unknown. On the Mac platform, Customize yields only one icon named "Bookmarks", but when that icon was dragged to the blank tool bar space immediately under the Navigation Toolbar, the name changed from Bookmarks to Bookmarks Toolbar and the entries displayed on the first mouse click. Thanks again.

Thanks for your reply. TonyE's suggestion solved the problem, but I'm going to Bookmark your suggested solution site for possible problems "down the line."

Thanks so much! Mine went away after an update and I have missed it. Just had time to hunt for an answer and this worked!