You can subscribe to your iCalendar feed so that Mozilla Thunderbird can stay up-to-date with your Remember The Milk tasks. You can choose to either display your tasks in the 'Tasks' section or on the calendar.

1. Find the iCalendar feed URL (to show tasks in the 'Tasks' section)

With this option, Thunderbird will display your tasks in the 'Tasks' section of the application (they will not appear on the calendar). You can choose to either subscribe to all of your lists or a single list.

Copy the tasks address iCalendar URL found by following the instructions here.

2. (Alternatively) Find the iCalendar feed URL (to show tasks on the calendar)

With this option you can export your tasks as events. This means that Thunderbird will display them on the calendar, rather than in the 'Tasks' section of the application. You can choose to either subscribe to all of your lists or a single list.

Copy the events address iCalendar URL found by following the instructions here.

3. Subscribe to the URL in Thunderbird

1. Click on 'File' menu.
2. Click on 'New' and select 'Calendar...'.
   
3. Select 'On the Network'.
4. Press 'Continue'.
   
5. Paste the iCalendar URL into the 'Location' box by right-clicking (or CTRL-clicking) on the box.
   
   
6. Press 'Continue'.
7. Give your calendar a name and choose a color.
8. Press 'Continue'.
   
9. Enter your Remember The Milk username and password if prompted.
10. Press 'OK'.
    
11. You should now see your tasks listed in the 'Tasks' section or displayed on the calendar in Thunderbird, depending on the iCalendar feed URL you used.