The default list of Favorites in the special character dialog as well the widget was created as the least common ground for all users. That makes not much sense and the default characters should be defined by the l10n teams.
from see also bug 120753 for increasing count of Favorites and Recents:
a mechanism of assigning the Favorites based on locale setting be implemented. Modify the locale DTD and incorporate the list of codepoints using XML for each locale--provided a default, but allow for l10n.
The split button UI should keep the 6 column format to keep width, but row count would grow for both.
*** Bug 123605 has been marked as a duplicate of this bug. ***