Ein paar Probleme

(function() {
    function doDatClock() {
        var timestr = new Date().toLocaleDateString( locale , options );
        
        const blanks = '     ';
        let i = timestr.lastIndexOf(',');
        timestr = timestr.substring(0,i) + blanks + timestr.substring(i+1);
        
        if( count == 1 ) {
            var counter = new Date( 1000 * sec ).toISOString().substr( 11 , 8 ); // .replace(/^[0:]+/, '') // if you want to replace zeroes and colons
            timestr = timestr + '       (' + counter + ')';
            sec++;
        }
        ClockLabel.setAttribute( 'value', timestr );
    }

    var count = 1; // if you don't want a counter set this to zero
    var agent = 1; // if you just want the clock set this to zero
    var language = 'de-DE'; // locale, e.g. 'de-DE' , 'en-US' , 'fr-FR'
    var personalText = ''; // your personal text here
    var cssColor = 'black'; // Font Color

    var css = 'margin-left: 30px; padding-top: 4px !important; padding-left: 0px; color: ' + cssColor + '; font-weight: 600; text-shadow: none; width: 275px;';
    var cssA = 'margin-left: 70px; width: auto;';

    var options = {
        weekday: 'long',
        year: 'numeric',
        month: 'long',
        day: 'numeric',
                   hour: '2-digit',
        minute: '2-digit',
        second: '2-digit'
    };

    var sec = 0;

    var locale = language || window.navigator.languages[0];

    var position = document.getElementById('helpMenu');

    var ClockLabel = document.createElement('label');
    ClockLabel.setAttribute('id', 'statusbar-clock-display');
    ClockLabel.setAttribute('class', 'statusbarpanel-text');
    ClockLabel.setAttribute('style', css);
    position.parentNode.insertBefore(ClockLabel, position.nextSibling);

    if( agent == 1 ) {
        var AgentLabel = document.createElement('label');
        AgentLabel.setAttribute('id', 'statusbar-agent-display');
        AgentLabel.setAttribute('class', 'statusbarpanel-text');
        AgentLabel.setAttribute('style', css + cssA);
        var FFstr = window.navigator.userAgent.split(' ');
        var FF = FFstr[FFstr.length-1].replace( '/' , ' ' );
        var text  = " Thunderbird - G  Profile " + AppConstants.MOZ_APP_VERSION_DISPLAY;
        AgentLabel.setAttribute( 'value', text );
        position.parentNode.insertBefore(AgentLabel, position.nextSibling);
    }

    if( count == 1 ) {
        ClockLabel.addEventListener('dblclick', function() { sec = 0; });
    }

    window.setInterval( doDatClock , 1000 );
})();