Problem is in:
if ($($curbox).next().attr('class') === 'box')
{
$('#content_navigator .box').hide();
$($curbox).next().fadeIn(1000);
$curbox = $($curbox).next();
}
else
{
$curbox = ('#content_navigator .box:first');
}
You switch to the first element, avoid displaying it, then move onto the next.
Change to the following:
if ($($curbox).next().attr('class') === 'box')
{
$('#content_navigator .box').hide();
$($curbox).next().fadeIn(1000);
$curbox = $($curbox).next();
}
else
{
$('#content_navigator .box').hide();
$('#content_navigator .box:first').fadeIn(1000);
$curbox = $('#content_navigator .box:first').next();
}
Also fixed your previous button. See at: http://jsbin.com/esame4/6/
Changed once again;. Made it more uniform throughout.