You can find this setting in "Settings -> General -> Startup". *https://support.mozilla.org/en-US/kb/firefox-Options-preferences-and-settings *https://support.mozilla.org/en-US/kb/restore-previous-session In case you use "Clear history when Firefox closes". *do not clear the Browsing History as this prevents restoring the tabs/windows *Settings -> Privacy & Security<br>Firefox will: "Use custom settings for history":<br>[X] "Clear history when Firefox closes" -> Settings *https://support.mozilla.org/en-US/kb/delete-browsing-search-download-history-firefox *clearing "Site Preferences" clears exceptions for cookies, images, pop-up windows, and software installation and exceptions for passwords and other website specific data *clearing "Cookies" will remove all cookies including cookies with an allow exception you may want to keep