Adding holidays to Calendar

Goto http://www.mozilla.org/projects/calendar/holidays.html (NB other sources are available: basically any site from which you can download an iCalendar (.ics, sometime mileadingly refered to as iCal) file with the data you require). Select the link for the nation of your choice.

Select Open with Calendar.

Decide whether to add to an existing calendar or create a new one; the latter allows you to delete en bloc and replace with more up-to-date versions should that bevome necessary).

Observe your calendar populated with holidays.