There is no time limit for the browsing history, only a maximum number of page that is calculated automatically to avoid performance issues. The download history should also be kept.<br /> I'm not sure about the search and saved form data as that data was removed silently in Firefox 3 versions.<br /> It looks that it is still only kept for 180 days, but you can override that with a pref browser.formfill.expire_days * http://blog.mozilla.com/dolske/2009/05/13/happy-form-history-expiration-day/ *http://mxr.mozilla.org/mozilla-central/source/toolkit/components/satchel/nsFormHistory.js#521