Using Mac OS X 10.8.2 (Mountain Lion) Firefox 17.01.
Each time it asked to to import bookmarks - I have done this numerous times - nothing gets imported (Safari).
Currently using Chrome because of this.
This happens if the profiles.ini is missing.
You can check the permissions of the folder that stores the file to make sure that you have write access.
Try to repair the disk permissions:
In Mac OS X v10.7 and later, the $HOME/Library folder is a hidden folder.
Open Finder and use one of these: