if(cookie && firstUsers[1]==='Pass') {
    alert("firstUsers is Pass");
} else {
    alert("expired / not set");
}

<script>

    function firstUsers(){
       days=1;
       myDate = new Date();
       myDate.setTime(myDate.getTime()+(days*24*60*60*1000));
       document.cookie = 'firstUsers=Pass; expires=' + myDate.toGMTString();
       document.cookie = 'secondUsers=Pass; expires=' + myDate.toGMTString();
    }

    var cookie = document.cookie.split(';')
        .map(function(x){ return x.trim().split('='); })
        .filter(function(x){ return x[0]==='firstUsers'; })
        .pop();

    if(cookie && firstUsers[1]==='Pass') {
        alert("firstUsers is Pass");
    } else {
        alert("expired / not set");
    }

    $('#set-btn').on('click', function(){
        // run code below

        firstUsers();
        return false;
    });


</script>