Make Firefox bookmarks visible only on new tab page, like Chrome

userChrome.css

/*
 * Bookmarks toolbar is visible only on new tab page, just like Chrome.
 *
 * Screenshot: https://vimeo.com/235059188
 * Video: https://vimeo.com/240436456
 *
 * Contributor(s): https://www.reddit.com/user/AJtfM7zT4tJdaZsm and Andrei Cristian Petcu
 *                 https://www.reddit.com/r/FirefoxCSS/comments/7evwow/show_bookmarks_toolbar_only_on_new_tab/
 */

/* https://superuser.com/a/1520406 */
#nav-bar:not(:focus-within) + #PersonalToolbar:not(:hover):not(:focus-within):not([customizing]) { visibility: collapse; }