diff --git a/xpcom/base/nsCycleCollector.cpp b/xpcom/base/nsCycleCollector.cpp
index 8b1a45748dd1..cbbbf80515d8 100644
--- a/xpcom/base/nsCycleCollector.cpp
+++ b/xpcom/base/nsCycleCollector.cpp
@@ -719,7 +719,7 @@ public:
         block->mNext = nullptr;
         mNextBlock = &block->mNext;
       }
-      return new (mNext++) PtrInfo(aPointer, aParticipant);
+      return new (mozilla::KnownNotNull, mNext++) PtrInfo(aPointer, aParticipant);
     }
   private:
     NodeBlock** mNextBlock;
diff --git a/xpcom/glue/PLDHashTable.cpp b/xpcom/glue/PLDHashTable.cpp
index 41e2a03c91f2..6152e90003c0 100644
--- a/xpcom/glue/PLDHashTable.cpp
+++ b/xpcom/glue/PLDHashTable.cpp
@@ -11,6 +11,7 @@
 #include "PLDHashTable.h"
 #include "mozilla/HashFunctions.h"
 #include "mozilla/MathAlgorithms.h"
+#include "mozilla/OperatorNewExtensions.h"
 #include "nsAlgorithm.h"
 #include "mozilla/Likely.h"
 #include "mozilla/MemoryReporting.h"
@@ -317,7 +318,7 @@ PLDHashTable::ClearAndPrepareForLength(uint32_t aLength)
   uint32_t entrySize = mEntrySize;
 
   this->~PLDHashTable();
-  new (this) PLDHashTable(ops, entrySize, aLength);
+  new (KnownNotNull, this) PLDHashTable(ops, entrySize, aLength);
 }
 
 void
diff --git a/xpcom/glue/nsCOMArray.cpp b/xpcom/glue/nsCOMArray.cpp
index 904cf70cb37c..3522f7b0d1e8 100644
--- a/xpcom/glue/nsCOMArray.cpp
+++ b/xpcom/glue/nsCOMArray.cpp
@@ -7,6 +7,7 @@
 #include "nsCOMArray.h"
 
 #include "mozilla/MemoryReporting.h"
+#include "mozilla/OperatorNewExtensions.h"
 
 #include "nsCOMPtr.h"
 
@@ -20,13 +21,13 @@ public:
   // Zero out the value
   static inline void Construct(E* aE)
   {
-    new (static_cast<void*>(aE)) E();
+    new (mozilla::KnownNotNull, static_cast<void*>(aE)) E();
   }
   // Invoke the copy-constructor in place.
   template<class A>
   static inline void Construct(E* aE, const A& aArg)
   {
-    new (static_cast<void*>(aE)) E(aArg);
+    new (mozilla::KnownNotNull, static_cast<void*>(aE)) E(aArg);
   }
   // Invoke the destructor in place.
   static inline void Destruct(E* aE)
diff --git a/xpcom/glue/nsTArray.h b/xpcom/glue/nsTArray.h
index e6dde16b4442..543c422cb356 100644
--- a/xpcom/glue/nsTArray.h
+++ b/xpcom/glue/nsTArray.h
@@ -18,6 +18,7 @@
 #include "mozilla/MathAlgorithms.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/Move.h"
+#include "mozilla/OperatorNewExtensions.h"
 #include "mozilla/ReverseIterator.h"
 #include "mozilla/TypeTraits.h"
 
@@ -504,7 +505,7 @@ public:
     // ints.  We don't want that because it can be a performance issue
     // and people don't expect it; nsTArray should work like a regular
     // C/C++ array in this respect.
-    new (static_cast<void*>(aE)) E;
+    new (mozilla::KnownNotNull, static_cast<void*>(aE)) E;
   }
   // Invoke the copy-constructor in place.
   template<class A>
@@ -515,7 +516,7 @@ public:
     static_assert(!mozilla::IsSame<E_NoCV*, A_NoCV>::value,
                   "For safety, we disallow constructing nsTArray<E> elements "
                   "from E* pointers. See bug 960591.");
-    new (static_cast<void*>(aE)) E(mozilla::Forward<A>(aArg));
+    new (mozilla::KnownNotNull, static_cast<void*>(aE)) E(mozilla::Forward<A>(aArg));
   }
   // Invoke the destructor in place.
   static inline void Destruct(E* aE) { aE->~E(); }
diff --git a/xpcom/glue/nsTHashtable.h b/xpcom/glue/nsTHashtable.h
index c2509e036a23..10d6435f059c 100644
--- a/xpcom/glue/nsTHashtable.h
+++ b/xpcom/glue/nsTHashtable.h
@@ -14,6 +14,7 @@
 #include "mozilla/MemoryChecking.h"
 #include "mozilla/MemoryReporting.h"
 #include "mozilla/Move.h"
+#include "mozilla/OperatorNewExtensions.h"
 #include "mozilla/PodOperations.h"
 #include "mozilla/TypeTraits.h"
 
@@ -391,7 +392,7 @@ nsTHashtable<EntryType>::s_CopyEntry(PLDHashTable* aTable,
   EntryType* fromEntry =
     const_cast<EntryType*>(static_cast<const EntryType*>(aFrom));
 
-  new (aTo) EntryType(mozilla::Move(*fromEntry));
+  new (mozilla::KnownNotNull, aTo) EntryType(mozilla::Move(*fromEntry));
 
   fromEntry->~EntryType();
 }
@@ -409,7 +410,7 @@ void
 nsTHashtable<EntryType>::s_InitEntry(PLDHashEntryHdr* aEntry,
                                      const void* aKey)
 {
-  new (aEntry) EntryType(static_cast<KeyTypePointer>(aKey));
+  new (mozilla::KnownNotNull, aEntry) EntryType(static_cast<KeyTypePointer>(aKey));
 }
 
 class nsCycleCollectionTraversalCallback;