That's an old pref and hasn't been around for years. You need to create a userChrome.css and copy / paste some code to achieve tabs on bottom. *https://www.userchrome.org/what-is-userchrome-css.html *https://www.userchrome.org/how-create-userchrome-css.html Code to paste below: <nowiki> /* Tab bar below Navigation & Bookmarks Toolbars For best results, show Title Bar or Menu Bar */ #nav-bar { /* main toolbar */ -moz-box-ordinal-group: 1 !important; border-top-width: 0 !important; } #PersonalToolbar { /* bookmarks toolbar */ -moz-box-ordinal-group: 2 !important; } #TabsToolbar { /* tab bar */ -moz-box-ordinal-group: 3 !important; } </nowiki> If you were a Classic Theme Restorer user, you can use the code below made by the developer of CTR. *https://raw.githubusercontent.com/Aris-t2/CustomCSSforFx/master/classic/css/tabs/tabs_below_navigation_toolbar.css