Table contents inside a popup dialog are not being read by the screen reader NVDA for firefox browser

Question

Click here to view the image This is what happens the blue marked area is read and nothing after that the red marked area is NVDA speech viewer where what is getting read is getting read. I have a non-empty table but the contents are not read by the NVDA screen reader when used with Firefox browser. It reads every other contents that comes before the table. Below is the sample code that is displayed on the Popup Dialog. Don't want to use role="presentation" as this solves the problem for not reading the table but the screen reader reads as if its a plain text and not as a table.

<div role="dialog">
    <h2>This is a H2 content. </h2>

    <p>This is a paragraph</p>

    <table style="width: 80%;">
    <caption class="offscreen">this is the caption for the table.</caption>
        <thead>
            <tr>
            <th style="width: 25%" scope="col">First Header</th>
            <th scope="col">Second Header</th>
            </tr> 
        </thead> 
        <tbody>
            <tr><td>C11</td><td>C21</td></tr>
            <tr><td>C21</td><td>C22</td></tr>
            <tr><td>C31</td><td>C32</td></tr>
            <tr><td>C41</td><td>C42</td></tr>
            <tr><td>C51</td><td>C52</td></tr>
        </tbody>
    </table>
</div>