Well fast to not like. Going back : unfortunately 56.0.2 and below is no longer safe to use for every day use do to security issues, but 52.5.3 ESR. It will continue to get security updates until May 2018, and you can download and install it from this page: *https://www.mozilla.org/en-US/firefox/organizations/all/ <b>Note : Legacy Extensions will be deleted or removed in any version update after May 2018</b>. You should make a backup of your Profile before going back and just because: *https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles *https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer Fyi: *https://www.howtogeek.com/333805/how-to-change-or-customize-firefoxs-new-tab-page/ *https://www.howtogeek.com/333110/how-to-customize-firefox-quantum-and-remove-the-white-space-around-the-title-bar/ and will miss out making it your : https://www.howtogeek.com/334716/how-to-customize-firefoxs-user-interface-with-userchrome.css/ http://techdows.com/2017/09/classic-theme-restorer-userchrome-css-modify-firefox-57-photon-ui.html https://github.com/Aris-t2/CustomCSSforFx/issues/1 https://www.accessfirefox.org/Theme-Font-Size-Changer.php https://www.userchrome.org/ https://www.accessfirefox.org/Firefox_Accessibility_Themes.php https://www.userchrome.org/what-is-userchrome-css.html http://kb.mozillazine.org/UserChrome.css https://github.com/axydavid/FirefoxUI/blob/master/README.md https://github.com/wilfredwee/photon-australis https://www.reddit.com/r/FirefoxCSS/ Note not all code in one place. Please let us know if this solved your issue or if need further assistance.