This article describes how to add a holiday calendar to the latest version of Lightning (a popular calendaring add-on for Thunderbird).
A holiday calendar lists all the public holidays of a country and displays these in Lightning. Many national holiday calendars are available on the Mozilla Holiday calendar page.
You can either download and import a calendar into Lightning or you can simply subscribe to a calendar by copying the URL and then adding it as a new remote calendar file.
With this method, the calendar file is stored on your hard disk and will be available even if you are offline. You will also be able to modify it (for example, by adding provincial or state holidays to a national holiday calendar).
Follow these steps to install a holiday calendar:
You will see that a new calendar with all your holidays has been added to your calendar view.
With this method, you will subscribe to a calendar file that is published on the internet. The calendar will be kept up to date by its maintainer.
Follow these steps to subscribe to a remote holiday calendar:
This will now load the holiday calendar. Lightning cannot determine when you are using a remote calendar, so you should double-click on the calendar name and check the box called Read Only in order to lock the calendar. If you don't do that, you will be able to change or delete any event, but all your changes will be lost when Thunderbird restarts.