As you know, Firefox's Library window only shows the date/time of the last visit, not the date/time of any earlier visits. This data is stored in Firefox (going back a certain amount of time), but in order to extract it, you would need to use an add-on or external program. I'm not familiar with programs for Mac, sorry.

Try this SQLite viewer and drop the places.sqlite file on the page..

• https://inloop.github.io/sqlite-viewer/

Some older threads with possible SQLite code:

• [/questions/937585] Support for "Date first visited" for history items was removed from Firefox
• [/questions/931864] Can I access all dates that a website has been visited?
• [/questions/945090] How can i prevent Firefox from overiding identical history entries?

SELECT url, title, visit_count, datetime(first_visit/1000000,'unixepoch','localtime') AS EarliestVisit, datetime(last_visit_date/1000000,'unixepoch','localtime') AS LatestVisit
FROM moz_places INNER JOIN
 (SELECT place_id, MIN(visit_date) AS first_visit
  FROM moz_historyvisits
  GROUP BY place_id) AS FirstVisits
 ON FirstVisits.place_id = moz_places.id
WHERE url LIKE '%mozilla.org%'
ORDER BY url