Sunbird: Password-protecting calendars?

Hey all,

I love this app, it's very useful to be able to take my calendar around with me! However, I'm a bit concerned, if I was to lose my memory key and someone found it, they would have access to all my appointments! So is there any way to password-protect a calendar? There is something about master passwords in the options menu but I can't figure it out.

Can anyone help?