I tried to make an accordion effect with JavaScript based off this video altering a few things like using an input button instead of a link for the selector. However for some reason it's not working. Firefox error console outputs unkown pseudo-class or pseudo-element "visible" everytime I try to use it. What's the problem?

$("div.example").hide();
$("input.exampleButton").click(function(){
    $("div.example:visible").slideUp("slow");
    $(this).parent().next().slideDown("slow");
    //return false; if you don't want the link to follow
});

Here is the HTML

input type="button" value="See An Example" class="exampleButton" />
<div class="example">
    ...content
</div>
input type="button" value="See An Example" class="exampleButton" />
<div class="example">
    ...content
</div>