1. Open the Remember The Milk web app.
2. Click on the Settings gear at the top right.
3. Click on Account Settings.
4. Click in to the Contact Preferences section.
5. Click on 'Add details'.
6. Select 'Desktop' from the drop-down.
7. Click 'Save changes'.
8. Ensure that the web app remains open.

Note: If you don't see 'Desktop' listed, be sure you're using a supported browser (at least Chrome 20 or Safari 6).