--- a/layout/generic/nsBlockDebugFlags.h
+++ b/layout/generic/nsBlockDebugFlags.h
@@ -1,22 +1,22 @@
 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #ifndef nsBlockDebugFlags_h__
 #define nsBlockDebugFlags_h__
 
-#undef NOISY_FIRST_LETTER         // enables debug output for first-letter specific layout
-#undef NOISY_FLOAT                // enables debug output for float reflow (the in/out metrics for the floated block)
-#undef NOISY_FLOAT_CLEARING
-#undef NOISY_FINAL_SIZE           // enables debug output for desired width/height computation, once all children have been reflowed
-#undef NOISY_REMOVE_FRAME
-#undef NOISY_COMBINED_AREA        // enables debug output for combined area computation
-#undef NOISY_BLOCK_DIR_MARGINS
-#undef NOISY_REFLOW_REASON        // gives a little info about why each reflow was requested
-#undef REFLOW_STATUS_COVERAGE     // I think this is most useful for printing, to see which frames return "incomplete"
-#undef NOISY_FLOATMANAGER         // enables debug output for float manager use, useful for analysing reflow of floats
-#undef NOISY_BLOCK_INVALIDATE     // enables debug output for all calls to invalidate
-#undef REALLY_NOISY_REFLOW        // some extra debug info
+#define NOISY_FIRST_LETTER         // enables debug output for first-letter specific layout
+#define NOISY_FLOAT                // enables debug output for float reflow (the in/out metrics for the floated block)
+#define NOISY_FLOAT_CLEARING
+#define NOISY_FINAL_SIZE           // enables debug output for desired width/height computation, once all children have been reflowed
+#define NOISY_REMOVE_FRAME
+#define NOISY_COMBINED_AREA        // enables debug output for combined area computation
+#define NOISY_BLOCK_DIR_MARGINS
+#define NOISY_REFLOW_REASON        // gives a little info about why each reflow was requested
+#define REFLOW_STATUS_COVERAGE     // I think this is most useful for printing, to see which frames return "incomplete"
+#define NOISY_FLOATMANAGER         // enables debug output for float manager use, useful for analysing reflow of floats
+#define NOISY_BLOCK_INVALIDATE     // enables debug output for all calls to invalidate
+#define REALLY_NOISY_REFLOW        // some extra debug info
 
 #endif // nsBlockDebugFlags_h__