Do you mean the browser.cache.check_doc_frequency pref on the <b>about:config</b> page? *http://kb.mozillazine.org/browser.cache.check_doc_frequency *http://kb.mozillazine.org/about:config ---- Type <b>about:config</b> in the location (address) bar and press the <i>Enter</i> key to open the <i>about:config</i> page like you open a website by typing the URL in the location bar. *If you see a warning message then you can confirm that you want to access the about:config page. *use the Search bar at the top of the about:config page to locate preferences more easily *preferences that have been modified and do not have the default value show as bold (user set) *preferences that are user set (bold) can be reset to the default value via the right-click context menu *preferences can be modified via the right-click context menu: Modify (String or Integer) or Toggle (Boolean) or by double-clicking the line with the pref