According to an answer to a similar question, those details don't appear. Have you seen them previously? There are preferences you can add to about:config to provide such information. I only have time showing because I don't keep history.

https://support.mozilla.org/en-US/questions/1308702

The Added and Last Modified columns are only for Bookmarks, but Firefox doesn't hide them when switching to History. Probably it should.

Edit: That is almost exactly what I said last time.

I'm pretty sure this info was available in previous versions (maybe a while ago) and it was often useful when chasing down a part-remembered search. It seems odd not to include it on the page as it is obviously available as the links are sorted in date order. Maybe there's an add-on that does the same. Thanks anyway Paul

Hi Paul, history is collapsed to a single row with a "Most Recent Visit" date/time. In the Places database, Firefox stores all the visits with their individual date/time but this isn't exposed in the Library window (you need to use an add-on or external program to list every visit).