In more detail
Each visit stores a URL, a title and a timestamp in the browser's own epoch (Chrome counts microseconds since 1601, Firefox since 1970), so an analyst must convert them correctly. Together the artifacts reconstruct what someone did and when. Most of them live in SQLite databases inside the user profile: Chrome's History file has a urls table and a visits table, Firefox keeps places.sqlite with moz_places and moz_historyvisits, and Safari uses History.db, which counts seconds since 2001.
Why it matters
A wrong epoch shifts every event by decades or by the time-zone offset, and a timeline built on it is useless. Clearing history is also rarely complete: deleted rows can survive in free database pages, the write-ahead log, the cache or the Cookie store, while private windows leave much less on disk.
Example
A Chrome urls row with last_visit_time = 13417954200000000:
13417954200000000 / 1000000 = 13417954200 s since 1601-01-01
13417954200 - 11644473600 = 1773480600 Unix seconds
= 2026-03-14 09:30:00 UTC
Firefox would store the same moment as 1773480600000000 (microseconds since 1970). The Browser Forensics does these conversions for you.