about:about Button

/* aboutabout_ToolbarButton.uc.js */
//  aboutabout-button.uc.js

  (function() {

       var css =`
    #aboutabout-ToolBarButton > image {
    display: none !important;
}

#aboutabout-ToolBarButton > label {
    display: flex !important;
    background-color: lightgreen !important;
    color: red !important;
    outline: 1px solid red !important;
    outline-offset: -1px !important;
}

#aboutabout-ToolBarButton:hover > label {
    background-color: green !important;
    color: cyan !important;
    outline: 1px solid purple !important;
    outline-offset: -1px !important;
}
  `;

  var sss = Cc['@mozilla.org/content/style-sheet-service;1'].getService(Ci.nsIStyleSheetService);
  var uri = makeURI('data:text/css;charset=UTF=8,' + encodeURIComponent(css));
  sss.loadAndRegisterSheet(uri, sss.AUTHOR_SHEET);

   if (location != 'chrome://browser/content/browser.xhtml') return;

    try {
        CustomizableUI.createWidget({
            id: 'aboutabout-ToolBarButton',
            type: 'custom',
            defaultArea: CustomizableUI.AREA_NAVBAR,
            onBuild: function(aDocument) {
                var toolbaritem = aDocument.createElementNS('http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul', 'toolbarbutton');
                var props = {
                    id: 'aboutabout-ToolBarButton',
                    class: 'toolbarbutton-1 chromeclass-toolbar-additional',
                    label: 'About:About',
                    tooltiptext: 'About:About',
                    /* style: 'list-style-image: ', */
                    //onclick: 'if (event.button == 0) { \
                    //                    openTrustedLinkIn("about:about", "tab");\
                    //             }; '
                };
                for (var p in props)
                    toolbaritem.setAttribute(p, props[p]);
                return toolbaritem;
            }
        });
    } catch(e) { };

    document.getElementById('aboutabout-ToolBarButton').addEventListener('click', event => {
    if (event.button === 0) {
         openTrustedLinkIn("about:about", "tab");
        }
    });

})();

        //            onclick: 'if (event.button == 0) { \
        //                    openTrustedLinkIn("about:about", "tab");\
        //                }; '
                };
                for (var p in props)
                    toolbaritem.setAttribute(p, props[p]);
        /* Neu */
                toolbaritem.addEventListener('click', event => {      
                    if (event.button == 0) { 
                        openTrustedLinkIn("about:about", "tab");
                    }
                });
        /* Bis hier */

                return toolbaritem;
            }
        });