Apparently, Firefox is supposed to handle this for you without any action on your part: http://blog.bonardo.net/2010/01/20/places-got-async-expiration http://b

Apparently, Firefox is supposed to handle this for you without any action on your part: http://blog.bonardo.net/2010/01/20/places-got-async-expiration http://blog.bonardo.net/2010/01/20/places-got-async-expirati... According to that post, Firefox now detects your system specs and chooses an appropriate history expiration time. The post also details a preference that allows you to tweak Firefox to retain a specific number of history entries (rather than a certain age).