IE和Mozilla Firefox 的兼容问题

            <tr style='display: none'>
                <td bgcolor="#F5F5F5">
                    设计方案载体：
                </td>
                <td>
                    <input name="ctl00$ContentPlaceHolder1$txtDesignCarrier" type="text" id="ctl00_ContentPlaceHolder1_txtDesignCarrier" size="60" />
                </td>
                <td class="notetext">
                </td>
            </tr>
我要从已知ctl00_ContentPlaceHolder1_txtDesignCarrier节点取“设计方案载体：”这几个字时
IE为$("ctl00_ContentPlaceHolder1_txtDesignCarrier").parentNode.parentNode.firstChild.innerHTML
可Mozilla Firefox 的值却为“undfind”。请问Mozilla Firefox 怎么取这个值