HTML not correctly parsed in Firefox and Chrome

HTML not correctly parsed in Firefox and Chrome

With this snippet of HTML, the topmost google link is included in every
element under it when shown in Firefox and Chrome.
<div>
<a href="http://www.google.com/">
<div>
<div>
<div>
<div>
<a>a tag</a>
</div>
<img />
<h3>a title</h3>
<p>a description</p>
<div>a detail</div>
</div>
</div>
</div>
</a>
</div>

What is causing this parsing issue and how can I fix it?