With the warning that I'm on Windows, not a Mac you might try deleting or (safer) renaming the directorys:
(I assume username in the above should be replaced with your Mac user name). The first is Fritzings temp files and the second is user parts (I'm assuming you don't have any user parts that you want to keep here, if you do keep a copy of the /Users/username/Documents/Fritzing/parts directory). These directories are not deleted by a reinstall (only the main Fritzing directory is) and on Windows they sometimes get corrupted (usually when I'm loading newly created parts with errors) and need to be cleared. When Fritzing restarts it will recreate the directories (empty). Otherwise perhaps another Mac user may have other suggestions (I haven't seen a complaint like this before though).