diff --git a/memory/build/replace_malloc_bridge.h b/memory/build/replace_malloc_bridge.h
index 20683c85df05..358d9f25c4b3 100644
--- a/memory/build/replace_malloc_bridge.h
+++ b/memory/build/replace_malloc_bridge.h
@@ -17,7 +17,7 @@
 // can decide to implement those methods or not.
 //
 // Replace-malloc libraries can provide such a bridge by implementing
-// a ReplaceMallocBridge-derived class, and a get_bridge function
+// a ReplaceMallocBridge-derived class, and a replace_get_bridge function
 // returning an instance of that class. The default methods in
 // ReplaceMallocBridge are expected to return values that callers would
 // understand as "the bridge doesn't implement this method", so that a
@@ -117,16 +117,6 @@ struct DMDFuncs;
 
 namespace phc {
 class AddrInfo;
-
-struct MemoryUsage {
-  // The amount of memory used for PHC metadata, eg information about each
-  // allocation including stacks.
-  size_t mMetadataBytes = 0;
-
-  // The amount of memory lost due to rounding allocation sizes up to the
-  // nearest page.  AKA internal fragmentation.
-  size_t mFragmentationBytes = 0;
-};
 }  // namespace phc
 
 // Callbacks to register debug file handles for Poison IO interpose.
@@ -136,10 +126,11 @@ struct DebugFdRegistry {
 
   virtual void UnRegisterHandle(intptr_t aFd);
 };
+
 }  // namespace mozilla
 
 struct ReplaceMallocBridge {
-  ReplaceMallocBridge() : mVersion(5) {}
+  ReplaceMallocBridge() : mVersion(4) {}
 
   // This method was added in version 1 of the bridge.
   virtual mozilla::dmd::DMDFuncs* GetDMDFuncs() { return nullptr; }
@@ -191,10 +182,6 @@ struct ReplaceMallocBridge {
   // This method was added in version 4 of the bridge.
   virtual bool IsPHCEnabledOnCurrentThread() { return false; }
 
-  // Return PHC memory usage information by filling in the supplied structure.
-  // This method was added in version 5 of the bridge.
-  virtual void PHCMemoryUsage(mozilla::phc::MemoryUsage& aMemoryUsage) {}
-
 #  ifndef REPLACE_MALLOC_IMPL
   // Returns the replace-malloc bridge if its version is at least the
   // requested one.
@@ -262,13 +249,6 @@ struct ReplaceMalloc {
     auto singleton = ReplaceMallocBridge::Get(/* minimumVersion */ 4);
     return singleton ? singleton->IsPHCEnabledOnCurrentThread() : false;
   }
-
-  static void PHCMemoryUsage(mozilla::phc::MemoryUsage& aMemoryUsage) {
-    auto singleton = ReplaceMallocBridge::Get(/* minimumVersion */ 5);
-    if (singleton) {
-      singleton->PHCMemoryUsage(aMemoryUsage);
-    }
-  }
 };
 #  endif
 
diff --git a/memory/replace/phc/PHC.cpp b/memory/replace/phc/PHC.cpp
index cd0f6322bb98..d86e9d37e662 100644
--- a/memory/replace/phc/PHC.cpp
+++ b/memory/replace/phc/PHC.cpp
@@ -656,12 +656,6 @@ class GMut {
                                 (kPageSize - 1));
     }
 
-    // The internal fragmentation for this allocation.
-    size_t FragmentationBytes() const {
-      MOZ_ASSERT(kPageSize >= UsableSize());
-      return mState == AllocPageState::InUse ? kPageSize - UsableSize() : 0;
-    }
-
     // The allocation stack.
     // - NeverAllocated: Nothing.
     // - InUse | Freed: Some.
@@ -725,15 +719,6 @@ class GMut {
     return page.UsableSize();
   }
 
-  // The total fragmentation in PHC
-  size_t FragmentationBytes() const {
-    size_t sum = 0;
-    for (auto page : mAllocPages) {
-      sum += page.FragmentationBytes();
-    }
-    return sum;
-  }
-
   void SetPageInUse(GMutLock aLock, uintptr_t aIndex,
                     const Maybe<arena_id_t>& aArenaId, uint8_t* aBaseAddr,
                     const StackTrace& aAllocStack) {
@@ -1404,11 +1389,6 @@ static size_t replace_malloc_usable_size(usable_ptr_t aPtr) {
   return gMut->PageUsableSize(lock, index);
 }
 
-static size_t metadata_size() {
-  return sMallocTable.malloc_usable_size(gConst) +
-         sMallocTable.malloc_usable_size(gMut);
-}
-
 void replace_jemalloc_stats(jemalloc_stats_t* aStats,
                             jemalloc_bin_stats_t* aBinStats) {
   sMallocTable.jemalloc_stats_internal(aStats, aBinStats);
@@ -1430,20 +1410,17 @@ void replace_jemalloc_stats(jemalloc_stats_t* aStats,
   }
   aStats->allocated += allocated;
 
-  // guards is the gap between `allocated` and `mapped`. In some ways this
-  // almost fits into aStats->wasted since it feels like wasted memory. However
-  // wasted should only include committed memory and these guard pages are
-  // uncommitted. Therefore we don't include it anywhere.
-  // size_t guards = mapped - allocated;
+  // Waste is the gap between `allocated` and `mapped`.
+  size_t waste = mapped - allocated;
+  aStats->waste += waste;
 
   // aStats.page_cache and aStats.bin_unused are left unchanged because PHC
   // doesn't have anything corresponding to those.
 
-  // The metadata is stored in normal heap allocations, so they're measured by
+  // gConst and gMut are normal heap allocations, so they're measured by
   // mozjemalloc as `allocated`. Move them into `bookkeeping`.
-  // They're also reported under explicit/heap-overhead/phc/fragmentation in
-  // about:memory.
-  size_t bookkeeping = metadata_size();
+  size_t bookkeeping = sMallocTable.malloc_usable_size(gConst) +
+                       sMallocTable.malloc_usable_size(gMut);
   aStats->allocated -= bookkeeping;
   aStats->bookkeeping += bookkeeping;
 }
@@ -1575,17 +1552,6 @@ class PHCBridge : public ReplaceMallocBridge {
     LOG("IsPHCEnabledOnCurrentThread: %zu\n", size_t(enabled));
     return enabled;
   }
-
-  virtual void PHCMemoryUsage(
-      mozilla::phc::MemoryUsage& aMemoryUsage) override {
-    aMemoryUsage.mMetadataBytes = metadata_size();
-    if (gMut) {
-      MutexAutoLock lock(GMut::sMutex);
-      aMemoryUsage.mFragmentationBytes = gMut->FragmentationBytes();
-    } else {
-      aMemoryUsage.mFragmentationBytes = 0;
-    }
-  }
 };
 
 // WARNING: this function runs *very* early -- before all static initializers
diff --git a/xpcom/base/moz.build b/xpcom/base/moz.build
index f685758b6fad..5576b3194c3c 100644
--- a/xpcom/base/moz.build
+++ b/xpcom/base/moz.build
@@ -220,9 +220,6 @@ if CONFIG["OS_TARGET"] == "Linux":
         "AvailableMemoryWatcherUtils.h",
     ]
 
-if CONFIG["MOZ_PHC"]:
-    DEFINES["MOZ_PHC"] = True
-
 GeneratedFile("ErrorList.h", script="ErrorList.py", entry_point="error_list_h")
 GeneratedFile(
     "ErrorNamesInternal.h", script="ErrorList.py", entry_point="error_names_internal_h"
diff --git a/xpcom/base/nsMemoryReporterManager.cpp b/xpcom/base/nsMemoryReporterManager.cpp
index 723cc6753205..de76bd7d8afb 100644
--- a/xpcom/base/nsMemoryReporterManager.cpp
+++ b/xpcom/base/nsMemoryReporterManager.cpp
@@ -1335,25 +1335,6 @@ class JemallocHeapReporter final : public nsIMemoryReporter {
     MOZ_COLLECT_REPORT(
       "heap-chunksize", KIND_OTHER, UNITS_BYTES, stats.chunksize,
       "Size of chunks.");
-
-#ifdef MOZ_PHC
-    mozilla::phc::MemoryUsage usage;
-    ReplaceMalloc::PHCMemoryUsage(usage);
-
-    MOZ_COLLECT_REPORT(
-      "explicit/heap-overhead/phc/metadata", KIND_NONHEAP, UNITS_BYTES,
-      usage.mMetadataBytes,
-"Memory used by PHC to store stacks and other metadata for each allocation");
-    MOZ_COLLECT_REPORT(
-      "explicit/heap-overhead/phc/fragmentation", KIND_NONHEAP, UNITS_BYTES,
-      usage.mFragmentationBytes,
-"The amount of memory lost due to rounding up allocations to the next page "
-"size. "
-"This is also known as 'internal fragmentation'. "
-"Note that all allocators have some internal fragmentation, there may still "
-"be some internal fragmentation without PHC.");
-#endif
-
     // clang-format on
 
     return NS_OK;