Remove the javascript and just add tabindex="0" to "a" tag.
<div class="large-9 columns">
<input type="text" class="txtsearchbox" name="txtsearch" id="txtsearch" placeholder="Search" />
</div>
<div class="large-3 columns">
<a tabindex="0" class="button expand" id="btnsearch1">
<img src="/Content/Images/search-16x16.png" id="btnsearch" />
</a>
</div>