play sounds when navigating in firefox

(function() {
    'use strict';

    function playSound() {
        var audio = new Audio('https://archive.org/download/windows-7-windows-media-Default-Sound/Media/Windows%20Navigation%20Start.wav'); // you can use this script anywhere, just change the url of the sound above
        audio.play();
    }

    function isLink(element) {
        return element.tagName === 'A';
    }

    function handleNewElements(elements) {
        elements.forEach(function(element) {
            if (isLink(element)) {
                element.addEventListener('mousedown', playSound);
            }
        });
    }

    var observer = new MutationObserver(function(mutations) {
        mutations.forEach(function(mutation) {
            if (mutation.type === 'childList') {
                handleNewElements(mutation.addedNodes);
            }
        });
    });

    observer.observe(document.body, { childList: true, subtree: true });

    handleNewElements(document.querySelectorAll('a'));
})();