Current Firefox versions keep a maximum number of visited page and do not have a time limit for the history. Firefox determines how many pages can be kept without affecting performance. In current releases you can find this value if the click "Verify Integrity" on the "Help -> More Troubleshooting Information" (about:support) page. * History can store a maximum of xxx unique pages You can create a new Number pref named places.history.expiration.max_pages if you want to override the automatically calculated number of pages. Be cautious though with modifying the value of this pref.