To configure Thunderbird to autocomplete email addresses by looking them up in OpenDS, follow these steps.
Import entries for your users into OpenDS.
See the Command Line Usage Guide for details.
Edit Thunderbird Preferences to use OpenDS for lookups.
Oddly enough I had manually to set
ldap_2.autoComplete.directoryServerusing the Advanced Configuration Config Editor.
Compose mail.
When you start typing an email address in the To: field, Thunderbird looks up that address in OpenDS.

