Code:
<form method="get" action="manufacturers.php">
<select style="width:100%;" name="manufacturerid" onchange="this.form.submit()">
<option value="0" selected>{$lng.lbl_manufacturers}...</option>
{section name=mid loop=$manufacturers_menu}
<option value="{$manufacturers_menu[mid].manufacturerid}">{$manufacturers_menu[mid].manufacturer}</option>
{/section}
</select>
</form>