When you search the date category disappears and all results for your search appears, whether you are in History Sidebar ("Ctrl+H"), or History Library List ("Ctrl+Shift+H").

Would suggest you use the History Library List, right click on a column heading or use the View menu there to show columns for: Name, Location, Visit Date, Visit Count, and then sort on Visit Date (includes time) if that is your interest by clicking on column header to sort ascending/descending

Unfortunately the same columns list must be used for History and for Bookmarks, so mine are

Name, Location, Parent Folder (from extension), Visit Date, Visit Count, Keyword, Description, Last Modified -- Some of the columns are not much wider than to let me know something is there.

See http://kb.mozillazine.org/Viewing_the_browsing_history_-_Firefox

If you visit a website from an older date via the history list then it is removed from that date and will become a new history entry for today and will no longer appear at the date where it previously appeared.

I do not understand why it should be removed from the history list - because that makes the history list untrue. Fair enough you go to it in the now but that does not mean that you did not go to it in the past. The history list should remain a true record.

If you visit a website more than once then the history list only shows the most recent visit and not the previous visits.

That is only true if you revisit via the history list. If I go to this website from your email it does not change my history. What you say may be true but it does not make it the right thing to do. History should be history and you should not be able to change it - deliberately or, as in this case, not. Is there a deep technical/software reason that it has to happen like this?

It is not the web page, but the link code that makes the difference. In the email you probably have an anchor to the last post appended and it that case it is a different URL that gets a new history entry.