For Postbox on Mac, helps make mail list easier to read.

userChrome.css

/* Adjust size of font use in Message Pane */
#threadTree treechildren:-moz-tree-cell-text {
font-size: 11pt !important;
}

/* Increase size of rows in Message Pane  */
#threadTree treechildren:-moz-tree-row {
height: 22px !important;
}

/* Add a light blue stripe to odd rows. */
#threadTree treechildren::-moz-tree-row(odd) {
background-color: #EDF3FE !important;
}

/* Make sure that odd rows still get the highlight color when you select them! */
#threadTree treechildren::-moz-tree-row(odd, selected) {
background-color: Highlight !important;
}