FireFox 33.0.3 and Input Type Select option:selected Not Working?

I need to 'reset' all the dropdowns on a form showing in Jquery-ui dialog.
The following code works with Chrome 38.0.2125.111 and IE 11.0.9600.17358 but NOT with FireFox 33.0.3...
I have two code examples and only use one and comment-out the other. Just wanted to show both...

[Jquery UI Dialog]

var $dialog = $('#myModal').dialog(
         {
             autoOpen: false,
             open: function (event, ui) {

             },
             close: function (event, ui) {
                 $('#form1 select option:first-child').attr('selected', 'selected');

                 $("#form1 select").each(function ()
                 {                     
                     $(this).find('option:first-child').attr("selected", "selected");
                 });
             },
             buttons: [
                 {
                     text: "Clear All",
                     width: "100",
                     click: function () {
                         $('select option:first-child').attr('selected', 'selected');

                         $("#form1 select").each(function () {
                             $(this).find('option:first-child').attr("selected", "selected");
                         });
                     }
                 }
             ]
         });

 <div id="myModal">
                <div>
                    <div>
                        <div>
                            <form id="form1">
                                <div class="form-group">
                                    <div class="col-sm-4">
                                        <label class="col-sm-3 control-label">Class</label>
                                        <select class="form-control" id="class" name="class">
                                            <option value="class">Any</option>
                                            <option value="class">Article</option>
                                            <option value="class">Conjunction</option>                                           
                                        </select>
                                    </div>
                                </div>
                                <div class="form-group">
                                    <div class="col-sm-4">
                                        <label class="col-sm-3 control-label">Case</label>
                                        <select class="form-control" id="case" name="case">
                                            <option value="case">Any</option>
                                            <option value="case">Accusative</option>
                                            <option value="case">Dative</option>                                            
                                        </select>
                                    </div>
                                </div>
                           </form>
                        </div>
                    </div>
                </div>
            </div>

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