找到了，這里有解決的方法
http://forums.mozillazine.org/viewtopic ... &t=3058570

首先要修改或增加布林參數
toolkit.legacyUserProfileCustomizations.stylesheets
設為true
然後以前的userChrome.css參數修改一下
下面是別人貼的，我試thunderbird 74有效，
自已再改成自已要的吧
/*
* Thunderbird userChrome
*
* Assign variable values paired with lightweight themes.
*/
:root {
/* Red > Charles Red =========================== */
/* --inbox-text: rgb(255,240,240);
--tab-bg-select: rgb(235,220,220);
--tab-bg-not-select: rgb(230,200,200);
--tab-select-text: green;
--tab-not-select-text: rgb(130,0,0);
--moz-row-even: rgb(120,10,10);
--moz-row-odd: rgb(100,5,10);
--tabs-bar: rgb(100,20,15);
--tabs-bar-gradient: rgb(210,20,40);
--mail-toolbox: rgb(80,10,5);
--mail-toolbox-gradient: rgb(190,10,30);
--list-header-bg: rgb(240,200,215);
--list-header-text: rgb(130,60,0);
--folderTree-bg: rgb(180,30,60);
--status-bar-top: rgb(200,30,20);
--status-bar-bottom: rgb(100,0,20);*/
/* Green > Dark Green ========================== */
/* --inbox-text: rgb(240,255,240);
--tab-bg-select: rgb(220,235,220);
--tab-bg-not-select: rgb(170,255,190);
--tab-select-text: green;
--tab-not-select-text: rgb(150,0,0);
--moz-row-even: rgb(10,120,65);
--moz-row-odd: rgb(5,90,55);
--tabs-bar: rgb(20,100,15);
--tabs-bar-gradient: rgb(5,210,170);
--mail-toolbox: rgb(10,80,5);
--mail-toolbox-gradient: rgb(5,180,100);
--list-header-bg: rgb(160,255,190);
--list-header-text: rgb(10,80,5);
--folderTree-bg: rgb(100,170,100);
--status-bar-top: rgb(10,150,80);
--status-bar-bottom: rgb(15,100,40);*/
/* Blue > Blue Transition ========================= */
/* --inbox-text: rgb(240,240,255);
--tab-bg-select: rgb(200,225,255);
--tab-bg-not-select: rgb(190,190,255);
--tab-select-text: green;
--tab-not-select-text: rgb(150,0,0);
--moz-row-even: rgb(10,80,190);
--moz-row-odd: rgb(10,60,140);
--tabs-bar: rgb(30,10,200);
--tabs-bar-gradient: rgb(5,170,210);
--mail-toolbox: rgb(15,20,100);
--mail-toolbox-gradient: rgb(5,100,180);
--list-header-bg: rgb(190,220,255);
--list-header-text: rgb(70,40,130);
--folderTree-bg: rgb(160,200,240);
--status-bar-top: rgb(30,70,210);
--status-bar-bottom: rgb(30,10,150);*/
/* Blue-Gold > Classic Blue ======================= */
/* --inbox-text: rgb(250,230,100);
--tab-bg-select: rgb(200,235,235);
--tab-bg-not-select: rgb(140,225,245);
--tab-select-text: green;
--tab-not-select-text: rgb(150,0,0);
--moz-row-even: rgb(25,90,140);
--moz-row-odd: rgb(25,70,120);
--tabs-bar: rgb(25,100,150);
--tabs-bar-gradient: rgb(20,180,220);
--mail-toolbox: rgb(25,70,120);
--mail-toolbox-gradient: rgb(50,100,200);
--list-header-bg: rgb(145,235,250);
--list-header-text: rgb(20,60,130);
--folderTree-bg: rgb(135,225,240);
--status-bar-top: rgb(20,140,200);
--status-bar-bottom: rgb(15,80,100);*/
/* Beige and Blue > Wood Feel ==================== */
--inbox-text: rgb(0,0,175);
--tab-bg-select: rgb(245,235,200);
--tab-bg-not-select: rgb(230,220,170);
--tab-select-text: green;
--tab-not-select-text: rgb(130,0,0);
--moz-row-odd: rgb(245,230,190);
--moz-row-even: rgb(235,220,175);
--tabs-bar: rgb(250,230,185);
--tabs-bar-gradient: rgb(250,250,200);
--mail-toolbox: rgb(240,220,150);
--mail-toolbox-gradient: rgb(250,250,200);
--list-header-bg: rgb(245,235,200);
--list-header-text: rgb(120,70,10);
--folderTree-bg: rgb(225,210,170);
--status-bar-top: rgb(220,200,150);
--status-bar-bottom: rgb(200,180,130);
} /* End variable declarations ====================== */
/*
* Increase UI font-sizes overall.
*/
* {-moz-appearance: none !important;
font-size: 18pt !important;
font-weight: bold !important;}
/*
* Change the bright white text color.
* Apply overall font/weight to inbox.
*/
treechildren::-moz-tree-cell-text {
-moz-appearance: none !important;
font-size: 18pt !important;
font-weight: bold !important;
color: var(--inbox-text) !important;}
/*
* Change background and text colors.
*/
#tabs-toolbar {
-moz-appearance: none !important;
background-image: linear-gradient(var(--tabs-bar-gradient),
transparent) !important;
color: var(--inbox-text) !important;}
#mail-toolbox {
-moz-appearance: none !important;
background: transparent !important;
background-image: linear-gradient(var(--mail-toolbox-gradient),
transparent) !important;
color: var(--mail-toolbox) !important;}
#button-getmsg, #button-compact, #button-addons, #qfb-show-filter-bar {
-moz-appearance: none !important;
color: var(--inbox-text) !important;
text-shadow: 0px 0px 0px #000 !important;}
/*#qfb-show-filter-bar {
-moz-appearance: none !important;
display: none !important;}*/
#quick-filter-bar-main-bar {
-moz-appearance: none !important;
background: beige !important;
color: blue !important;}
#threadTree {
-moz-appearance: none !important;
background: var(--list-header-bg) !important;}
treecol {
-moz-appearance: none !important;
color: var(--list-header-text) !important;}
#folderTree {
-moz-appearance: none !important;
background: var(--folderTree-bg) !important;}
#status-bar {
-moz-appearance: none !important;
background-image: linear-gradient(var(--status-bar-top),
var(--status-bar-bottom)) !important;
color: var(--inbox-text) !important;
text-shadow: 0px 0px 0px #000 !important;}
/*
* Change active tab background to match subject line.
*/
.tab-background[selected="true"] {
-moz-appearance: none !important;
background: var(--tab-bg-select) !important;}
/*
* Change inactive tab background to complement.
*/
.tab-background:not([selected="true"] ) {
-moz-appearance: none !important;
background: var(--tab-bg-not-select) !important;}
/*
* Change tab-text colors.
*/
.tab-text[selected="true"] {
-moz-appearance: none !important;
font-weight: bold !important;
color: var(--tab-select-text) !important;
text-shadow: 0px 0px 0px #000 !important;}
.tab-text:not([selected="true"] ) {
-moz-appearance: none !important;
font-weight: bold !important;
color: var(--tab-not-select-text) !important;
text-shadow: 0px 0px 0px #000 !important;}
/*
* Center tab text horizontally and vertically.
*/
.tab-text {
-moz-appearance: none !important;
-moz-box-flex: 1 !important;
margin-top: 2px !important;
margin-bottom: -2px !important;
text-align: center !important;
margin-left: -20px !important;}
/*
* Make tab close button black, enlarge, center.
*/
#tabs-toolbar .tab-close-button {
-moz-appearance: none !important;
transform: scale(1.3);
margin-top: 1px !important;
margin-bottom: -1px !important;
color: rgb(0,0,0) !important;}
/*
* Enlarge sidebar text.
*/
#folderTree treechildren::-moz-tree-cell-text {
-moz-appearance: none !important;
font-size: 18pt !important;}
/*
* Modify Inbox line spacing.
*/
treechildren::-moz-tree-row {
-moz-appearance: none !important;
height: 32px !important;}
/*
* Alternate Inbox line colors.
*/
treechildren::-moz-tree-row(even),
treechildren:hover::-moz-tree-row(even) {
-moz-appearance: none !important;
background: var(--moz-row-even) !important;}

treechildren::-moz-tree-row(odd),
treechildren:hover::-moz-tree-row(odd) {
-moz-appearance: none !important;
background: var(--moz-row-odd) !important;}

treechildren::-moz-tree-row(selected, focus),
treechildren:hover::-moz-tree-row(selected, focus) {
-moz-appearance: none !important;
background: Highlight !important;}

treechildren::-moz-tree-cell-text(selected, focus),
treechildren:hover::-moz-tree-cell-text(selected, focus) {
-moz-appearance: none !important;
color: HighlightText !important;}
/*
* Change mail header colors.
*/
#expandedHeaderView {
text-shadow: 0px 0px 0px #000 !important;
color: blue !important;
background: beige !important;}
/*
* End Thunderbird.userChrome
*/