diff --git a/intl/locale/DateTimeFormat.cpp b/intl/locale/DateTimeFormat.cpp
index 162a3d4d5ac8..45fa9c9a9f6b 100644
--- a/intl/locale/DateTimeFormat.cpp
+++ b/intl/locale/DateTimeFormat.cpp
@@ -81,6 +81,12 @@ nsresult DateTimeFormat::FormatDateTime(
     case Skeleton::yyyyMMMM:
       skeleton.AssignASCII("yyyyMMMM");
       break;
+    case Skeleton::E:
+      skeleton.AssignASCII("E");
+      break;
+    case Skeleton::EEEE:
+      skeleton.AssignASCII("EEEE");
+      break;
     default:
       MOZ_ASSERT_UNREACHABLE("Unhandled skeleton enum");
   }
diff --git a/intl/locale/DateTimeFormat.h b/intl/locale/DateTimeFormat.h
index 5d9a77529d8a..6e675b36a995 100644
--- a/intl/locale/DateTimeFormat.h
+++ b/intl/locale/DateTimeFormat.h
@@ -37,7 +37,8 @@ class DateTimeFormat {
 
   enum class Style { Wide, Abbreviated };
 
-  enum class Skeleton { yyyyMM, yyyyMMMM };
+  // Weekday (E, EEEE) only used in Thunderbird.
+  enum class Skeleton { yyyyMM, yyyyMMMM, E, EEEE };
 
   // performs a locale sensitive date formatting operation on the PRTime
   // parameter
diff --git a/intl/locale/tests/gtest/TestDateTimeFormat.cpp b/intl/locale/tests/gtest/TestDateTimeFormat.cpp
index e2e56014cfb3..06b2810e7bc9 100644
--- a/intl/locale/tests/gtest/TestDateTimeFormat.cpp
+++ b/intl/locale/tests/gtest/TestDateTimeFormat.cpp
@@ -223,6 +223,16 @@ TEST(DateTimeFormat, DateFormatSelectorsForeign)
   ASSERT_TRUE(NS_SUCCEEDED(rv));
   ASSERT_STREQ("Januar 1970", NS_ConvertUTF16toUTF8(formattedTime).get());
 
+  rv = mozilla::DateTimeFormat::FormatDateTime(
+      &prExplodedTime, DateTimeFormat::Skeleton::E, formattedTime);
+  ASSERT_TRUE(NS_SUCCEEDED(rv));
+  ASSERT_STREQ("Do", NS_ConvertUTF16toUTF8(formattedTime).get());
+
+  rv = mozilla::DateTimeFormat::FormatDateTime(
+      &prExplodedTime, DateTimeFormat::Skeleton::EEEE, formattedTime);
+  ASSERT_TRUE(NS_SUCCEEDED(rv));
+  ASSERT_STREQ("Donnerstag", NS_ConvertUTF16toUTF8(formattedTime).get());
+
   rv = mozilla::DateTimeFormat::GetCalendarSymbol(
       mozilla::DateTimeFormat::Field::Month,
       mozilla::DateTimeFormat::Style::Wide, &prExplodedTime, formattedTime);