Firefox only shows the most recent visit in the History Manager, earlier visits are saved but are hidden, so this is likely about page you visited in the past and have visited recently. If you would go back before the first visit or select a month where you didn't visit them then you shouldn't see them.

You can look at this NirSoft utility to inspect or backup history:

• https://www.nirsoft.net/utils/browsing_history_view.html

OK, you're right. So if those earlier visits are in the history, but hid, is there any way I can see them?

Thanks for the link.

But what do Copy and Paste do, that are in the menu of the history?

For History, you can (only) copy an History item to a Bookmarks folder or to an editor that accepts HTML code, you can't paste to add new history. Internally this goes via JSON (text/x-moz-place), but there is also text/html and text/unicode on the clipboard.

Thanks, so that means I can't edit the History except to delete things, and there's no way to see previous visits to a site?

I don't understand what Restore is supposed to do. I see that it gives me a bunch of possible restores, each one specified by a date (every few months), each saying something like "32.2 kB -- 36 items". I have no idea what that is.

Restore is to roll back to an earlier automatic bookmark backup; there is no restore for history.

To export a full visit-by-visit history, I use this program:

http://www.nirsoft.net/utils/mozilla_history_view.html

Possibly there is an add-on to do it, which might have a better interface.