Refs #3252 Update Thunderbird icon and name

Mozilla Thunderbird with User Agent "Mozilla/5.0 (Windows NT 5.1; rv:13.0) Gecko/20120614 Thunderbird/13.0.1" is currently shown with the red Mozilla lizard icon, instead of the blue(ish) icon of Thunderbird, and it will be shown as "Mozilla 13.0" instead of "Thunderbird 13.0". (Unlike Firefox, which is shown as "Firefox 13.0" with respective Firefox icon.)