--- mozilla-2.0.orig/memory/mozalloc/mozalloc.cpp
+++ mozilla-2.0/memory/mozalloc/mozalloc.cpp
@@ -237,7 +237,7 @@
         return 0;
 
 #if defined(MOZ_MEMORY)
-    return malloc_usable_size(ptr);
+    return 0;
 #elif defined(XP_MACOSX)
     return malloc_size(ptr);
 #elif defined(XP_WIN)