diff --git a/mozilla/xpcom/tests/StringFactoringTests/StringTestDebug.Prefix b/mozilla/xpcom/tests/StringFactoringTests/StringTestDebug.Prefix
new file mode 100755
index 00000000000..3724af942db
--- /dev/null
+++ b/mozilla/xpcom/tests/StringFactoringTests/StringTestDebug.Prefix
@@ -0,0 +1,4 @@
+#include "StringTest.Prefix"
+
+#define DEBUG 1
+#undef NDEBUG