This may be a persistent and old bug in FF and wasn't specifically addressed in the original bug report (Bug 889661), with duplicates being non-congruent.
It appears that occasionally when adding a bookmark to a longer bookmark toolbar folder, either by dragging a URL or through the context menu, and then manually modifying (dragging) that bookmark to a new position in the vertical folder list, all toolbar menu lists lose mouse wheel scrollability. This behavior is then permanent.
The second behavior described in bug 889661 where the list does not autoscroll when a bookmark is attempted to be moved to a position outside the visible range within the toolbar folder is NOT observed. This functionality works.
The lost functionality is not restored in Safe Mode.
Anybody with a suggestion on which files to restore to fix this corruption?