HTML ラベルでテキストの選択を防ぐにはどうすればよいですか?

.unselectable {
    -webkit-touch-callout: none;
    -webkit-user-select: none;
    -khtml-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
}

<label class="unselectable">Unselectable Label</label>

function disableSelection(element) {
    if (typeof element.onselectstart != 'undefined') {
        element.onselectstart = function() { return false; };
    } else if (typeof element.style.MozUserSelect != 'undefined') {
        element.style.MozUserSelect = 'none';
    } else {
        element.onmousedown = function() { return false; };
    }
}

disableSelection(document.querySelector("label"));

$.fn.disableSelection = function() { 
    this.each(function() {  
        disableSelection(this);
    }); 
};

$("label").disableSelection();