You can toggle the bookmarks sidebar on/off via "Ctrl+B". You can find a Sidebars button in the Customize palette and drag it on the Navigation Toolbar. The checkbox for showing the Bookmarks Toolbar is a sub menu with three choices: *"Always Show", "Only Show on New Tab", "Never Show" "Only Show on New Tab" only applies to the "about:newtab" and "about:home" pages, so won't work when the new tab page is not set to the default Firefox Home screen.