You'll need to make changes to the fields in your content type.
StringField('firstName', widget=StringWidget( label="First Name", ), index='FieldIndex:schema', );
The part in bold is what you'll need to do for your field in the content type.
Next you'll need to specify in site setup of your plone instance that you want smart folders to use it.
- Go to site setup
- Click "Smart Folder Settings"
- Select "smart folder metadata" tab
- Click "all fields"
- Find the field you just added and give it a new name(by default it uses its getter name)