--- a/memory/replace/dmd/DMD.cpp
+++ b/memory/replace/dmd/DMD.cpp
@@ -262,18 +262,16 @@ Plural(size_t aN)
 
 // Used by calls to Show().
 static const size_t kBufLen = 64;
 static char gBuf1[kBufLen];
 static char gBuf2[kBufLen];
 static char gBuf3[kBufLen];
 static char gBuf4[kBufLen];
 
-static const size_t kNoSize = size_t(-1);
-
 //---------------------------------------------------------------------------
 // Options (Part 1)
 //---------------------------------------------------------------------------
 
 class Options
 {
   template <typename T>
   struct NumOption
@@ -1442,17 +1440,19 @@ public:
 
   // This is |const| thanks to the |mutable| fields above.
   void Add(const Block& aB) const
   {
     mNumBlocks++;
     mRecordSize.Add(aB);
   }
 
-  static const char* const kRecordKind;   // for PrintSortedRecords
+  // For PrintSortedRecords.
+  static const char* const kRecordKind;
+  static bool recordsOverlap() { return false; }
 
   void Print(const Writer& aWriter, LocationService* aLocService,
              uint32_t aM, uint32_t aN, const char* aStr, const char* astr,
              size_t aCategoryUsableSize, size_t aCumulativeUsableSize,
              size_t aTotalUsableSize) const;
 
   static int QsortCmp(const void* aA, const void* aB)
   {
@@ -1551,17 +1551,19 @@ public:
   static int QsortCmp(const void* aA, const void* aB)
   {
     const FrameRecord* const a = *static_cast<const FrameRecord* const*>(aA);
     const FrameRecord* const b = *static_cast<const FrameRecord* const*>(aB);
 
     return RecordSize::Cmp(a->mRecordSize, b->mRecordSize);
   }
 
-  static const char* const kRecordKind;   // for PrintSortedRecords
+  // For PrintSortedRecords.
+  static const char* const kRecordKind;
+  static bool recordsOverlap() { return true; }
 
   // Hash policy.
 
   typedef const void* Lookup;
 
   static uint32_t hash(const void* const& aPc)
   {
     return mozilla::HashGeneric(aPc);
@@ -1935,18 +1937,19 @@ PrintSortedRecords(const Writer& aWriter
       r->Print(aWriter, aLocService, i+1, numRecords, aStr, astr,
                aCategoryUsableSize, cumulativeUsableSize, aTotalUsableSize);
     } else if (i == maxRecords) {
       W("%s: stopping after %s stack %s records\n\n", aStr,
         Show(maxRecords, gBuf1, kBufLen), kind);
     }
   }
 
-  MOZ_ASSERT(aCategoryUsableSize == kNoSize ||
-             aCategoryUsableSize == cumulativeUsableSize);
+  // This holds for TraceRecords, but not for FrameRecords.
+  MOZ_ASSERT_IF(!Record::recordsOverlap(),
+                aCategoryUsableSize == cumulativeUsableSize);
 }
 
 static void
 PrintSortedTraceAndFrameRecords(const Writer& aWriter,
                                 LocationService* aLocService,
                                 const char* aStr, const char* astr,
                                 const TraceRecordTable& aTraceRecordTable,
                                 size_t aCategoryUsableSize,
@@ -1978,18 +1981,19 @@ PrintSortedTraceAndFrameRecords(const Wr
       FrameRecordTable::AddPtr p = frameRecordTable.lookupForAdd(pc);
       if (!p) {
         FrameRecord fr(pc);
         (void)frameRecordTable.add(p, fr);
       }
       p->Add(tr);
     }
   }
+
   PrintSortedRecords(aWriter, aLocService, aStr, astr, frameRecordTable,
-                     kNoSize, aTotalUsableSize);
+                     aCategoryUsableSize, aTotalUsableSize);
 }
 
 // Note that, unlike most SizeOf* functions, this function does not take a
 // |nsMallocSizeOfFun| argument.  That's because those arguments are primarily
 // to aid DMD track heap blocks... but DMD deliberately doesn't track heap
 // blocks it allocated for itself!
 //
 // SizeOfInternal should be called while you're holding the state lock and while

--- a/memory/replace/dmd/test-expected.dmd
+++ b/memory/replace/dmd/test-expected.dmd
@@ -126,29 +126,29 @@ Unreported: 2 blocks in stack trace reco
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Unreported stack frame records
 ------------------------------------------------------------------
 
 Unreported: 9 blocks from 1 stack trace record in stack frame record M of N
  1,008 bytes (900 requested / 108 slop)
- 8.34% of the heap;  0.00% of unreported
+ 8.34% of the heap;  81.82% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: 2 blocks from 1 stack trace record in stack frame record M of N
  112 bytes (112 requested / 0 slop)
- 0.93% of the heap;  0.00% of unreported
+ 0.93% of the heap;  9.09% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: 2 blocks from 1 stack trace record in stack frame record M of N
  112 bytes (112 requested / 0 slop)
- 0.93% of the heap;  0.00% of unreported
+ 0.93% of the heap;  9.09% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Once-reported stack trace records
 ------------------------------------------------------------------
 
 Once-reported: 1 block in stack trace record 1 of 11
@@ -251,53 +251,53 @@ Once-reported: 1 block in stack trace re
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Once-reported stack frame records
 ------------------------------------------------------------------
 
 Once-reported: 1 block from 1 stack trace record in stack frame record M of N
  8,192 bytes (4,097 requested / 4,095 slop)
- 67.77% of the heap;  0.00% of once-reported
+ 67.77% of the heap;  77.40% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Once-reported: 1 block from 1 stack trace record in stack frame record M of N
  1,024 bytes (1,023 requested / 1 slop)
- 8.47% of the heap;  0.00% of once-reported
+ 8.47% of the heap;  9.67% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Once-reported: 1 block from 1 stack trace record in stack frame record M of N
  512 bytes (512 requested / 0 slop)
- 4.24% of the heap;  0.00% of once-reported
+ 4.24% of the heap;  4.84% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Once-reported: 4 blocks from 3 stack trace records in stack frame record M of N
  416 bytes (416 requested / 0 slop)
- 3.44% of the heap;  0.00% of once-reported
+ 3.44% of the heap;  3.93% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Once-reported: 4 blocks from 3 stack trace records in stack frame record M of N
  416 bytes (416 requested / 0 slop)
- 3.44% of the heap;  0.00% of once-reported
+ 3.44% of the heap;  3.93% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Once-reported: 1 block from 1 stack trace record in stack frame record M of N
  16 bytes (10 requested / 6 slop)
- 0.13% of the heap;  0.00% of once-reported
+ 0.13% of the heap;  0.15% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Once-reported: 1 block from 1 stack trace record in stack frame record M of N
  8 bytes (0 requested / 8 slop)
- 0.07% of the heap;  0.00% of once-reported
+ 0.07% of the heap;  0.08% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Summary
 ------------------------------------------------------------------
 
 Total:                12,088 bytes (100.00%) in      30 blocks (100.00%)
@@ -363,29 +363,29 @@ Unreported: 6 blocks in stack trace reco
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Unreported stack frame records
 ------------------------------------------------------------------
 
 Unreported: 9 blocks from 1 stack trace record in stack frame record M of N
  1,008 bytes (900 requested / 108 slop)
- 35.49% of the heap;  0.00% of unreported
+ 35.49% of the heap;  48.84% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: 6 blocks from 1 stack trace record in stack frame record M of N
  528 bytes (528 requested / 0 slop)
- 18.59% of the heap;  0.00% of unreported
+ 18.59% of the heap;  25.58% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: 6 blocks from 1 stack trace record in stack frame record M of N
  528 bytes (528 requested / 0 slop)
- 18.59% of the heap;  0.00% of unreported
+ 18.59% of the heap;  25.58% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Once-reported stack trace records
 ------------------------------------------------------------------
 
 Once-reported: 1 block in stack trace record 1 of 4
@@ -425,35 +425,35 @@ Once-reported: 1 block in stack trace re
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Once-reported stack frame records
 ------------------------------------------------------------------
 
 Once-reported: 1 block from 1 stack trace record in stack frame record M of N
  512 bytes (512 requested / 0 slop)
- 18.03% of the heap;  0.00% of once-reported
+ 18.03% of the heap;  74.42% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Once-reported: 1 block from 1 stack trace record in stack frame record M of N
  80 bytes (79 requested / 1 slop)
- 2.82% of the heap;  0.00% of once-reported
+ 2.82% of the heap;  11.63% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Once-reported: 1 block from 1 stack trace record in stack frame record M of N
  80 bytes (78 requested / 2 slop)
- 2.82% of the heap;  0.00% of once-reported
+ 2.82% of the heap;  11.63% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Once-reported: 1 block from 1 stack trace record in stack frame record M of N
  16 bytes (10 requested / 6 slop)
- 0.56% of the heap;  0.00% of once-reported
+ 0.56% of the heap;  2.33% of once-reported
  PC is
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Summary
 ------------------------------------------------------------------
 
 Total:                 2,840 bytes (100.00%) in      27 blocks (100.00%)
@@ -521,53 +521,53 @@ Unreported: ~1 block in stack trace reco
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Unreported stack frame records
 ------------------------------------------------------------------
 
 Unreported: ~4 blocks from ~1 stack trace record in stack frame record M of N
  ~512 bytes (~512 requested / ~0 slop)
- 35.96% of the heap;  0.00% of unreported
+ 35.96% of the heap;  35.96% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: 1 block from 1 stack trace record in stack frame record M of N
  256 bytes (256 requested / 0 slop)
- 17.98% of the heap;  0.00% of unreported
+ 17.98% of the heap;  17.98% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: 1 block from 1 stack trace record in stack frame record M of N
  144 bytes (144 requested / 0 slop)
- 10.11% of the heap;  0.00% of unreported
+ 10.11% of the heap;  10.11% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: 1 block from 1 stack trace record in stack frame record M of N
  128 bytes (128 requested / 0 slop)
- 8.99% of the heap;  0.00% of unreported
+ 8.99% of the heap;  8.99% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: ~1 block from ~1 stack trace record in stack frame record M of N
  ~128 bytes (~128 requested / ~0 slop)
- 8.99% of the heap;  0.00% of unreported
+ 8.99% of the heap;  8.99% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: ~1 block from ~1 stack trace record in stack frame record M of N
  ~128 bytes (~128 requested / ~0 slop)
- 8.99% of the heap;  0.00% of unreported
+ 8.99% of the heap;  8.99% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 Unreported: ~1 block from ~1 stack trace record in stack frame record M of N
  ~128 bytes (~128 requested / ~0 slop)
- 8.99% of the heap;  0.00% of unreported
+ 8.99% of the heap;  8.99% of unreported
  PC is
    ... RunTestMode ... DMD.cpp
 
 ------------------------------------------------------------------
 Once-reported stack trace records
 ------------------------------------------------------------------
 
 (none)