Before clicking "Done", you must add something to the new custom toolbar for it to remain. You can even drag a "Separator" or "Space" or "Flexible space" from the customize palette to the toolbar to have it hold with no other items on the toolbar. Also be sure that the name that you assign to the new toolbar is checked (displayed). Create a new toolbar - https://support.mozilla.org/en-US/kb/customize-firefox-controls-buttons-and-toolbars?esab=a&s=custom+toolbar&r=0&as=s#w_how-can-i-add-extra-toolbars Displaying toolbars ('''''applies to all toolbars, not just Navigation toolbar''''') - https://support.mozilla.org/en-US/kb/navigation-buttons-missing#w_showing-the-navigation-toolbar