You can look at these prefs on the about:config page. http://kb.mozillazine.org/browser.history_expire_days (180) (also affects saved form data) http://kb.mozillazine.org/browser.history_expire_days_min (90) .......... http://kb.mozillazine.org/browser.history_expire_sites (40000) http://kb.mozillazine.org/browser.history_expire_visits (20000) ---- To open the ''about:config'' page, type '''about:config''' in the location (address) bar and press the Enter key, just like you type the url of a website to open a website. If you see a warning then you can confirm that you want to access that page.