Can only "Add Item" if Encrypt is Unchecked.
Then after save&close & re-open, most but not all 'saved' entries were lost.
Retrying, reinstalling, deleting all preferences & reinstalling, downloading the latest from your website instead of addons.mozilla.org, trying the latter again & reinstalling & reinstalling after having cleared all preferences... did not work either.
All this was attempted by first creating & assigning categories.
For now I've switched back to PEO, but Really Want POP's Encryption protection.
I'm using ff26.0 on mackbook pro, let me know what other info you need to diagnose=)
Much thanks in advance ~JJL