Hey @nereli I like your extension and I also made some small changes, I added a hover color :

I have made these changes :

extension.js
line 29 to 39 :

            if(Key%2){

                var Bg = ' id="even"';
            }else{

                var Bg = ' id="odd"';

            }

            //alert("Key: " + Key + "\nTitle: " + Title + "\nTime:" + Time + "\nName:" + Name + "\nSubject Url:" + SubjectUrl);
            Datas = Datas + '<div' + Bg +'><a href="https://steemit.com' + SubjectUrl + '" target="_blank" >' + Title + ' (' + Name + ' - ' + Time + ')</a></div>';

I added style.css file
style.css
body{

font-family: arial;
font-size: 12px;
}
#odd a{
text-decoration: none;
color: #333;
font-weight: bold;
font-size: 13px;
border-bottom: 1px dashed #cecece;
display: block;
padding: 4px 2px;
}
#even a{
text-decoration: none;
color: #333;
font-weight: bold;
font-size: 13px;
border-bottom: 1px dashed #cecece;
display: block;
padding: 4px 2px;
background-color: #efefef;
}

#odd a:hover {
background-color: #6797e5;
}

#even a:hover {
background-color: #6797e5;
}

steemit.html

add to head :   <link rel="stylesheet" href="style.css">