Organize your schedule and life's important events in a calendar that's fully integrated with your Thunderbird email. Manage multiple calendars, create your daily to do list, invite friends to events, and subscribe to public calendars.
Allows bidirectional access to Google Calendar
ReminderFox displays and manages lists of reminders and ToDo's. ReminderFox makes sure you remember all of your important dates via easy-to-use lists, alerts, and alarms, right in your browser without the need for a separate calendar program.
Google and Zimbra contact sync for Thunderbird. (TB 24 and above NOT supported)
OpenMedSpel for Mozilla Firefox, Thunderbird, and SeaMonkey is free and open source medical spell checking dictionary that includes nearly 50,000 medical terms ranging from abdominis to zygomatic.