Ein Script, "QuickLinkButton-about-about.uc.js", habe ich noch.

//  Button_aboutabout.uc.js
//  öffnet Dialog about:about

(function() {

  if (!window.gBrowser)
	return;

      // Start User Einstellungen
      
      let btn_id = 'about_button';  // Button #id
      const btn_icon = 'a3.png';  // Name+Dateiendung des Symbols
      const iconPath = 'file:///C:/FoxIcons2/';  // Pfad zum Ordner der das Icon beinhaltet
      const ImagePath = iconPath + btn_icon;  // Kompletter Pfad zum Icon =>
      const btn_label = 'about:about';  // Bezeichnung
      const btn_tooltiptext = 'Dialog about:about öffnen';  // Tooltip
      
      // User Einstellungen Ende

      // Button
    	try {
          CustomizableUI.createWidget({
             id: btn_id,
             defaultArea: CustomizableUI.AREA_NAVBAR,
             label: btn_label,
             tooltiptext: btn_tooltiptext,
             onCreated: (this_button) => {
                this_button.style.MozContextProperties = 'fill, stroke, fill-opacity, stroke-opacity';
                this_button.style.listStyleImage = 'url("' + ImagePath + '")';
                this_button.style.minWidth = 'fit-content';
             }
          });
    	} catch(e) {}

      function click_button() {
          document.getElementById(btn_id).addEventListener('click', event => {
              if (event.button === 0) {
				 openTrustedLinkIn("about:about", "tab");
              }
			});
          };

      if (window.readyState !== "loading") {
    		setTimeout(click_button, 500);
        }
      else {
    	  window.addEventListener( "DOMContentLoaded", click_button );
        };
      window.addEventListener('aftercustomization', () => {
    		setTimeout(() => click_button(), 100)
        });

})();

// aboutaboutButton.uc.js
// öffnet den Dialog about:about

(function() {
  if (!window.gBrowser) return;

  let btn_id = 'about-about-button';

  try {
    CustomizableUI.createWidget({
      id: btn_id,
      defaultArea: CustomizableUI.AREA_NAVBAR,
      label: "about:about",
      tooltiptext: "Dialog about:about aufrufen",
      onCreated: (this_button) => {
        this_button.style.MozContextProperties = 'fill, stroke, fill-opacity, stroke-opacity'; 
        this_button.style.listStyleImage = 'url("file:///C:/FoxIcons/a2.ico")';
        this_button.style.minWidth = 'fit-content';
      }
    });
  } catch (e) {}

  function addClickListener(btn) {
    if (btn.hasAttribute('listener-added')) return; 
    btn.setAttribute('listener-added', 'true');
    btn.addEventListener("click", event => {
      if (event.button === 0) openTrustedLinkIn("about:about", "tab");
    });
  }

  let observer = new MutationObserver(() => {
    let btn = document.getElementById(btn_id);
    if (btn && !btn.hasAttribute('listener-added')) {
      addClickListener(btn);
    }
  });
  observer.observe(document.documentElement, { childList: true, subtree: true });

  let btn = document.getElementById(btn_id);
  if (btn) addClickListener(btn);
})();

// QuickLinkButton-about:about.uc.js  =  Button_for_QuickLinks-about.uc.js
// Das Script erstellt einen Button, der einen Tab öffnet mit den Links zu verschiedenen "about:"-Seiten.

// Source file https://www.camp-firefox.de/forum/thema/140072/?postID=1282691#post1282691

/* ----------------------------------------------------------------------------------- */
/*     Zu beachten ist, dass die Grafiken sich im richtigen Ordner befinden müssen     */
/*            %appdata%\Mozilla\Firefox\Profiles\"Profilname"\chrome\icons             */
/* ----------------------------------------------------------------------------------- */

(function() {

  if (!window.gBrowser)
	return;

   const
   // ■■ START UserConfiguration ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■
            id = 'link-button-about', // Id des Buttons
          link = 'about:about', // Linkziel des Buttons
         label = 'Quicklink: about:about', // Bezeichnung des Buttons
   tooltiptext = 'Quicklink:\nabout:about',
   // Icon-------------------------------------------------------
          icon = 'firefox.svg',  // [Name.Dateiendung] des Symbols
      iconPath = '/chrome/icons/', // Pfad zum Ordner der das Icon beinhaltet
   // ■■ END UserConfiguration ■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■
   curProfDir = PathUtils.toFileURI(PathUtils.join(PathUtils.profileDir));

	if (Services.prefs.getBoolPref('svg.context-properties.content.enabled') == false) {
		Services.prefs.setBoolPref('svg.context-properties.content.enabled', true );
	}
   //BUTTON
	try {
      CustomizableUI.createWidget({
         id: id,
         defaultArea: CustomizableUI.AREA_NAVBAR,
         label: label,
         tooltiptext: tooltiptext,

         onCreated: (button) => {
            button.style.MozContextProperties = 'fill, stroke, fill-opacity';
            button.style.listStyleImage = 'url("' + curProfDir + iconPath + icon + '")';
            button.style.minWidth = 'fit-content';
            button.style.fill = '#f1b508'; // Farbe für das SVG-Icon setzen
         }
      });
	} catch(e) {};

   // click
   (function add_button() {
   const button = document.getElementById(id);

   if (button) {
      button.addEventListener('click', (event) => {
         if (event.button === 0) {
         event.target.ownerGlobal.openTrustedLinkIn(link, "tab");
         }
      });
   } else {
      setTimeout(add_button, 100);
   }
   })();

})();