Nel foglio di stile userChrome.css , che devi inserire sotto la directory
%appdata%\Thunderbird\Profiles\xvcwauzd.default\chrome
copia e incolla il codice qui sotto (modificando i colori a tuo piacimento)
l'ultimo paragrafo "Change the color of containing folders" è totalmente commentato (si può vedere dai tag /* e */ del paragrafo treechildren
/* ----- font red color - new mail in the left (accounts) pane --- */
treechildren:-moz-tree-cell-text(folderNameCol, newMessages-true) {
color: blue !important; /* red */ }
/* ---- to make the account name in a colour when new messages arrive --- */
treechildren::-moz-tree-cell-text(folderNameCol, biffState-NewMail,
isServer-true),
treechildren::-moz-tree-cell-text(folderNameCol, specialFolder-Inbox,
newMessages-true) { font-weight: bold !important; color: blue!important;
/* red */ }
/* ------- has new unread messages ----- */
treechildren::-moz-tree-cell-text(container, closed, hasUnread, read) {
text-decoration: underline; color: blue !important; /* red */ }
/* Change the color of containing folders */
/* treechildren::-moz-tree-cell-text(hasUnreadMessages-true) {color: blue
!important;} */