--- a/mail/themes/linux/mail/compose/messengercompose.css
+++ b/mail/themes/linux/mail/compose/messengercompose.css
@@ -212,17 +212,17 @@ menulist:-moz-locale-dir(rtl) > .menulis
   border-top: none;
 }
 
 #attachments-box {
   padding-top: 5px;
 }
 
 #attachmentBucketSize {
-  color: #888a85;
+  color: GrayText;
   padding-inline-end: 1px;
 }
 
 /* ::::: attachment reminder ::::: */
 
 #attachmentNotificationBox b {
   font-weight: bold;
 }
@@ -478,16 +478,21 @@ treechildren::-moz-tree-image(subscribed
   -moz-context-properties: fill;
   fill: currentColor;
 }
 
 #msgIdentity[editable="true"] > .menulist-dropmarker {
   display: none;
 }
 
+#msgIdentityPopup > menuitem[_moz-menuactive="true"] > .menu-description {
+  color: HighlightText;
+  opacity: .7;
+}
+
 /* ::::: format toolbar ::::: */
 
 #FormatToolbar {
   -moz-appearance: none;
   color: WindowText;
   margin-left: 3px;
   margin-right: 3px;
   background-image: url("chrome://messenger/skin/messengercompose/linux-noise.png");

--- a/mail/themes/osx/mail/compose/messengercompose.css
+++ b/mail/themes/osx/mail/compose/messengercompose.css
@@ -274,32 +274,37 @@ toolbar[brighttext] #button-print {
 #msgIdentity[editable="true"] > menupopup > menuitem {
   -moz-appearance: menuitem;
 }
 
 #msgIdentityPopup {
   margin-inline-start: initial;
 }
 
+#msgIdentityPopup > menuitem[_moz-menuactive="true"] > .menu-description {
+  color: HighlightText;
+  opacity: .7;
+}
+
 #addresses-box {
   margin: 4px 6px;
 }
 
 #attachments-box {
   padding-top: 5px;
 }
 
 #attachmentbucket-sizer {
   border-top: none;
   border-bottom: none;
   height: 7px;
 }
 
 #attachmentBucketSize {
-  color: #888a85;
+  color: GrayText;
 }
 
 /* ::::: attachment reminder ::::: */
 
 #attachmentNotificationBox b {
   font-weight: bold;
 }
 

--- a/mail/themes/windows/mail/compose/messengercompose.css
+++ b/mail/themes/windows/mail/compose/messengercompose.css
@@ -88,16 +88,21 @@
     background-color: -moz-field;
     -moz-border-top-colors: ThreeDShadow ThreeDHighlight;
     -moz-border-right-colors: ThreeDShadow ThreeDHighlight;
     -moz-border-bottom-colors: ThreeDShadow ThreeDHighlight;
     -moz-border-left-colors: ThreeDShadow ThreeDHighlight;
   }
 }
 
+#msgIdentityPopup > menuitem[_moz-menuactive="true"] > .menu-description {
+  color: HighlightText;
+  opacity: .7;
+}
+
 /* ::::: attachment reminder ::::: */
 
 #attachmentReminderText {
   margin-inline-start: 0;
   cursor: pointer;
 }
 
 #attachmentKeywords {
@@ -790,17 +795,17 @@ toolbar[brighttext] #button-print {
   background-color: transparent;
 }
 
 #attachments-box {
   padding-top: 4px;
 }
 
 #attachmentBucketSize {
-  color: #888a85;
+  color: GrayText;
 }
 
 #attachmentNotificationBox b {
   font-weight: bold;
 }
 
 #attachmentNotificationBox > notification[image="null"] .messageImage {
   background-image: url("chrome://messenger/skin/icons/attach.svg");