I find it a frequent occurrence to want to schedule another similar appointment. For example, if you have a doctor's appointment, you'll often need to schedule another appointment in the future. All things are essentially the same - same doctor, same office, etc - j just a different date and time. I select the current appointment, right-click and select copy, right-click again and select paste. Since I have more than one calendar (a home calendar and a work calendar), Thunderbird prompts me on which calender to write this pasted event. Might I suggest it paste it into the calendar from whence the copied event came? This would eliminate that step. After pasting I have the same appointment on the same day and time. I can right-click and select Edit and adjust the day and time. I can even select a different calendar from the drop-down if I need to. I think it would be better if another option was on the right-click menu such that instead of selecting Copy you select something like Schedule New Occurrence. Select that and immediately the Edit Event dialog box should popup allowing you to schedule your next doctors appointment.