You just need to untick the holiday calendar that is shown in the calendar pane

There is no holiday calendar shown in the calendar pane that I can see. All I see is my "home" calendar. How do I find what you are talking about?

Thanks for the screenshot. In my set up I have two separate calendars that Thunderbird (actually Lightning) subscribes to, I thought you might have multiple calendars too. Since you don't, the unwanted entries are within your 'home' calendar itself. Where is that hosted? Is that a calendar kept entirely on your own machine -- i.e. is this a calendar that you created from scratch in Lightning, and all the entries are ones you have put in yourself? Or is this a calendar provided e.g. by Google or Yahoo, i.e. it's an external calendar which you can access via a browser and which is synchronised with Lightning on your machine? In my case, both of my calendars are part of my Gmail account. When I set them up, Google 'helpfully' (!) added in a holiday calendar as well and I had a whole lot of events that I didn't want. I had to log in to my Google account to turn that holiday calendar off. In other words it wasn't something that Thunderbird had put in, it was external.

As far as I know this calendar is entirely on my PC and the events are ones I entered except for the holidays.

OK, thank you for the explanation. Looking closely at your screenshot I notice that the holidays are shown as (untimed) 'events' with a border, unlike the timed events/appointments for each day. I notice also that there are some other untimed 'events' (e.g. for 5 and 6 March) which also have a border, and those two also have a reminder set. I'm wondering, therefore, if the untimed 'events' shown with a border are actually tasks? I'm feeling my way here because personally I use a Lightning add-on which displays my tasks in a separate pane, so I don't have a calendar display that looks anything like yours. If your holiday 'events' are actually tasks, then you should be able to edit them by going to the 'Events and Tasks' menu and selecting 'Tasks'. How they got into your calendar in the first place I have no idea. Since you have entered all the data yourself (i.e. it does not come from a remote service like Google) I guess that at some point you may have imported a calendar file. However I hope that we are working towards a way for you to remove it.

The un-timed events on the 5th and 6th of March are all day events so they have no time of day attached to them. I entered them. The entry on the 16th of Feb. is also an event. You are correct at one time I imported at least one Holiday "list" from Mozilla back when the calendar was a standalone program not part of Firefox. Do you know how to find all entries that came from this kind of import and where I can get a good Holiday file from. It needs to be one that understands how Holidays really work.

Hi again and thanks for this information, I now understand what has happened. I can't think of a quick and easy way to remove the holidays, I'm afraid. The process of importing them has mixed them up among the other entries you have made and you'll just have to remove them manually, which is tiresome. However I suspect that they have been imported as repeating events. That's how holiday calendars usually work. So if you open (e.g.) the President's Day event as if to edit it, you should find that it's set to repeat annually. (I assume that's how often that holiday occurs?) If so, when you delete it, you should get the option to 'delete all occurrences'. Select that and you'll remove that holiday for this and all future years. I can't advise where to get a good holiday calendar from, I don't use one myself. There's a page here about it: https://support.mozilla.org/en-US/kb/adding-a-holiday-calendar. If you search on the internet you will find other holiday files in the .ics format that Thunderbird can import. What I would strongly advise, though, before you do that, is to create a new calendar in Thunderbird, and then import the holidays into that! The two calendars -- your own 'home' calendar and the new one -- will display together, so in the monthly/weekly/daily view you will see the entries from both of them; but -- crucially -- the computer will treat them as separate datasets. That way you can choose whether to display one or both of them (by ticking the box in the calendar list), whether or not to retain either of them (by deleting them from the calendar list), and what colour you want each of them to have in the display (by editing the calendar properties). You can have several calendars at once and it's a much more flexible and reliable way to manage Thunderbird than by putting everything (appointments, tasks, memos, holidays etc.) into one calendar.