Auch ich nutze in 57.0 Aborix-Lösung
Im Script OpenNewTab.uc.js wird mir bei Aufruf in Notepad++ diese Passage dunkel unterlegt angezeigt:
Code
		
					
				`{
		var b_bookmarks = true;
		var b_history = true;
		if (!e) return 'current';
		var win = window.opener || window;
		if (win.isTabEmpty(win.gBrowser.mCurrentTab)) return 'current';
		var node = e.originalTarget;
		if (node.matches('.bookmark-item'))
			return b_bookmarks ? 'tab' : 'current';
		while (node) {
			switch (node.id) {
				case 'bookmarksMenuPopup':  // menubar bookmarks
				case 'BMB_bookmarksPopup':  // navibar bookmarks
				case 'bookmarksPanel':      // sidebar bookmarks
					return b_bookmarks ? 'tab' : 'current';
				case 'goPopup':             // menubar history
				case 'PanelUI-history':     // navibar history
				case 'history-panel':       // sidebar history
					return b_history ? 'tab' : 'current';
				case 'placeContent':        // library bookmarks&history
					var collection = window.document.getElementById('searchFilter').getAttribute('collection');
					var tab = collection === "bookmarks" && b_bookmarks || collection === "history" && b_history;
					return tab ? 'tab' : 'current';
			}
			node = node.parentNode;
		}
		return 'current';
    }`; 
		
		
	 
															
		 Also ohne UserChrome.js Erweiterung ....
 Also ohne UserChrome.js Erweiterung ....