diff --git a/testing/mozharness/configs/unittests/thunderbird_extra.py b/testing/mozharness/configs/unittests/thunderbird_extra.py
index d23a53c97d..5a21cb9fea 100644
--- a/testing/mozharness/configs/unittests/thunderbird_extra.py
+++ b/testing/mozharness/configs/unittests/thunderbird_extra.py
@@ -22,7 +22,7 @@ config = {
         "mochitest-browser-chrome-thunderbird": [
             "--flavor=browser",
             "--subsuite=thunderbird",
-            "--leak-threshold=125829120",
-        ],  # 120MB
+            "--leak-threshold=104857600",  # 100MB
+        ],
     },
 }