Deleting your Preference File in OS X
From Miro User Documentation
1. Shutdown Miro
2. Navigate to the Support directory:
Mac HD/users/_username_/library/preferences/
3. Delete the org.participatorycuture.miro.plist file
4. Restart Miro
Note: For a total uninstall, delete the "/users/_username_/library/appilcation support/miro" folder.

