table嵌套table 滚动条 IE8自动扩展 火狐缩进,该怎么处理

<table align="center" width="300px" cellpadding="0" cellspacing="0" border="0">

    <tr>

        <td>

            <table>

                <tr>

                    <td>

                        <asp:GridView id="gvHeader" runat="server" allowsorting="True" autogeneratecolumns="False">

                                <HeaderStyle CssClass="gvHeader" />

                                <Columns>

                                    <asp:BoundField HeaderText="序号">

                                        <HeaderStyle Width="30" />

                                    </asp:BoundField>

                                    <asp:BoundField HeaderText="编码" SortExpression="ShowCode">

                                        <HeaderStyle Width="100" />

                                    </asp:BoundField>

                                </Columns>

                            </asp:gridview>

                        <div id="divMain" style="overflow: auto; height: 250px;">

                            <asp:GridView id="gvBody" runat="server" autogeneratecolumns="False" showheader="False">

                                    <SelectedRowStyle CssClass="gvSelectedRow" />