thunderbird/chrome/userChrome.css

* {
  font-size: 10pt !important;
}

#threadTree tbody {
	color: #373737;
}

#threadTree tbody tr {
	opacity: 0.5;
}

#threadTree tbody tr[data-properties~="tagged"],
#threadTree tbody tr[data-properties~="unread"] {
	opacity: 1;
}