Need to get the exact time that you visited a page in Firefox? I couldn't find an easy way to look this up in the History interface, or anywhere else for that matter. I did however know that Firefox stores this kind of thing in sqlite3 databases. Here's how I got what I needed.
First you have to find the sqlite databases, I'm on Linux so that would be in my home directory. The database you want is places.sqlite. Crack that open in sqlite3. Your command will differ as this is based on your profile name, mine is "gmail" so I ended up with g69ap5lc.gmail.
$ sqlite3 ~/.mozilla/firefox/g69ap5lc.gmail/places.sqlite
Be aware you have to shut down the Firefox instance first, because it locks the file. Make sure your privacy settings won't erase it all when you shut it down! I had to change mine to "Remember history" first.
Next you need to find and grab the timestamp. This can be a chore if you don't have the full URL. I was looking for the one from spiffie.org below.
sqlite>.headers on sqlite>select * from moz_places; id|url|title|rev_host|visit_count|hidden|typed|favicon_id|frecency|last_visit_date 1|http://www.mozilla.com/en-US/firefox/central/|/en-US/firefox/central/|moc.allizom.www.|0|0|0||140| ... 1366|http://spiffie.org/kits/usb7/driver_linux.shtml|Linux USB7 Driver|gro.eiffips.|1|0|0||100|1261169238197827
The column we are interested in is last_visit_date which is 1261169238197827 in our case. You can also list all the recent visits from the moz_historyvisits table with the id column.
sqlite> select * from moz_historyvisits where place_id = '1366'; id|from_visit|place_id|visit_date|visit_type|session 200|199|1366|1261169238197827|6|42
Now we need to convert that timestamp into something we can read (unless you are a super UNIX geek and can read timestamps). This instance is too precise for the date command, so lop off the first 10 digits and use that, so in the example we use 1261169238.
$ date -d @1261169238 Fri Dec 18 14:47:18 CST 2009
Not short and sweet, but it works.