在JavaScript中拖放多个文件，Firefox无法正常工作

Question

我需要从Thunderbird程序中拖放多个文件。 它适用于谷歌浏览器，但对于Firefox我只能拖放一个来自雷鸟的电子邮件。 我的代码如下：

  <div class="container">
    <div class="row">
            <div id="result"></div>
            <div align="center">
                <div id="dock" class="dock">Drag & Drop Emails Here</div>
            </div>
        </div>
    </div>

<script type="text/javascript">
    $(document).ready(function() {
        // Add eventhandlers for dragover and prevent the default actions for this event
        $('#dock').on('dragover', function(e) {
            $(this).attr('class', 'dock_hover'); // If drag over the window, we change the class of the #dock div by "dock_hover"
            e.preventDefault();
            e.stopPropagation();
        });

        // Add eventhandlers for dragenter and prevent the default actions for this event
        $('#dock').on('dragenter', function(e) {
            e.preventDefault();
            e.stopPropagation();
        });

        $('#dock').on('dragleave', function(e) {
            $(this).attr('class', 'dock'); // If drag OUT the window, we change the class of the #dock div by "dock" (the original one)
        });
        // When drop the files
        $('#dock').on('drop', function(e){ // drop-handler event
            if (e.originalEvent.dataTransfer) {
                //alert(e.originalEvent.dataTransfer.files.length);
                if (e.originalEvent.dataTransfer.files.length) { // Check if we have files
                    e.preventDefault();
                    e.stopPropagation();
                    // Launch the uploads function
                    upload(e.originalEvent.dataTransfer.files); // Access the dropped files with e.originalEvent.dataTransfer.files
                }
            }
        });
        function upload(files){ // uploads function
            var fd = new FormData(); // Create a FormData object
            //alert("upload");

            for (var i = 0; i < files.length; i++) { // Loop all files
                fd.append('file_' + i, files[i]); // Create an append() method, one for each file dropped
            }
            fd.append('nbr_files', i); // The last append is the number of files
            $.ajax({ // JQuery Ajax
                type: 'POST',
                url: sJSUrlImportEmails, // URL to the PHP file which will insert new value in the database
                data: fd, // We send the data string
                processData: false,
                contentType: false,
                success: function(data) {
                    $('#result').html($("#text_import_success").text());
                    $('#dock').attr('class', 'dock'); // #dock div with the "dock" class
                }
            });
        }
    });

</script>

为了保存文件，我使用FormData。 我怎样才能解决我的问题？也许Firefox有一些选择？感谢。