Firefox does not have a feature to import history from an HTML file. It can import bookmarks from a specially formatted HTML file, but not history.

iMazing is for iOS, not MacOS. Is the history on your iPhone/iPad, or on your Mac?

I found an article explaining how to extract history from Safari's History.db file. It's very interesting to me, a person that often needs to look inside databases, but it doesn't exactly cut to the chase with solution for you:

http://2016.padjo.org/tutorials/sqlite-your-browser-history/

I tried to put that learning into effect in a web app that simply creates an HTML table of your entire history, but I don't have a file to test with, so it's a bit of an orphan for the time being. If you want to try it, feel free:

https://www.jeffersonscher.com/res/safarihistoryextractor.html

Expect slow rendering at best, and most likely complete failure.

I think that the HTML doesn't need to be formatted. A simple file with only <A HREF> type links should be sufficient. I don't know how Safari stores its bookmarks. In Firefox you can do a Copy and Paste to copy selected history to bookmarks. I don't know if you can do similar in Safari and then export the bookmarks to an HTML file.

Jefferson Scher, what a clear and helpful (and quick) response. I appreciate the lengths you went to, to understand my issue and to respond with such a useful briefing / set of directions.

I followed each step and was able to find and drag the History.db file as you indicated. It was 24 MB. I clicked after dragging to get it to apparently go off and create an .HTML file... but after 1 hour and 30 some minutes it does NOT seem to have come to an end. Where should I go look for the output .HTML file? I did not see a prompt, yet, to create the file.

I will leave this running overnight to see if it is simply slow.

You probably have a SQLite utility on your Mac that you can use. Such a utility can likely handle big databases more efficient.

You can use the query as posted on the web page or use the query Jefferson used on his page.

SELECT datetime(visit.visit_time + 978307200, 'unixepoch', 'localtime') as visited, visit.title, page.url
FROM history_visits visit INNER JOIN history_items page ON page.id = visit.history_item
ORDER BY visit.visit_time DESC, page.url