diff --git a/ipc/chromium/src/base/pickle.h b/ipc/chromium/src/base/pickle.h
index 759f0f06a9c8..ee2c7cb18053 100644
--- a/ipc/chromium/src/base/pickle.h
+++ b/ipc/chromium/src/base/pickle.h
@@ -92,36 +92,37 @@ class Pickle {
   // the Pickle, initialize *iter to NULL.  If successful, these methods return
   // true.  Otherwise, false is returned to indicate that the result could not
   // be extracted.
-  MOZ_MUST_USE bool ReadBool(PickleIterator* iter, bool* result) const;
-  MOZ_MUST_USE bool ReadInt16(PickleIterator* iter, int16_t* result) const;
-  MOZ_MUST_USE bool ReadUInt16(PickleIterator* iter, uint16_t* result) const;
-  MOZ_MUST_USE bool ReadShort(PickleIterator* iter, short* result) const;
-  MOZ_MUST_USE bool ReadInt(PickleIterator* iter, int* result) const;
-  MOZ_MUST_USE bool ReadLong(PickleIterator* iter, long* result) const;
-  MOZ_MUST_USE bool ReadULong(PickleIterator* iter,
-                              unsigned long* result) const;
-  MOZ_MUST_USE bool ReadInt32(PickleIterator* iter, int32_t* result) const;
-  MOZ_MUST_USE bool ReadUInt32(PickleIterator* iter, uint32_t* result) const;
-  MOZ_MUST_USE bool ReadInt64(PickleIterator* iter, int64_t* result) const;
-  MOZ_MUST_USE bool ReadUInt64(PickleIterator* iter, uint64_t* result) const;
-  MOZ_MUST_USE bool ReadDouble(PickleIterator* iter, double* result) const;
-  MOZ_MUST_USE bool ReadIntPtr(PickleIterator* iter, intptr_t* result) const;
-  MOZ_MUST_USE bool ReadUnsignedChar(PickleIterator* iter,
-                                     unsigned char* result) const;
-  MOZ_MUST_USE bool ReadString(PickleIterator* iter, std::string* result) const;
-  MOZ_MUST_USE bool ReadWString(PickleIterator* iter,
-                                std::wstring* result) const;
-  MOZ_MUST_USE bool ReadBytesInto(PickleIterator* iter, void* data,
-                                  uint32_t length) const;
-  MOZ_MUST_USE bool ExtractBuffers(
+  [[nodiscard]] bool ReadBool(PickleIterator* iter, bool* result) const;
+  [[nodiscard]] bool ReadInt16(PickleIterator* iter, int16_t* result) const;
+  [[nodiscard]] bool ReadUInt16(PickleIterator* iter, uint16_t* result) const;
+  [[nodiscard]] bool ReadShort(PickleIterator* iter, short* result) const;
+  [[nodiscard]] bool ReadInt(PickleIterator* iter, int* result) const;
+  [[nodiscard]] bool ReadLong(PickleIterator* iter, long* result) const;
+  [[nodiscard]] bool ReadULong(PickleIterator* iter,
+                               unsigned long* result) const;
+  [[nodiscard]] bool ReadInt32(PickleIterator* iter, int32_t* result) const;
+  [[nodiscard]] bool ReadUInt32(PickleIterator* iter, uint32_t* result) const;
+  [[nodiscard]] bool ReadInt64(PickleIterator* iter, int64_t* result) const;
+  [[nodiscard]] bool ReadUInt64(PickleIterator* iter, uint64_t* result) const;
+  [[nodiscard]] bool ReadDouble(PickleIterator* iter, double* result) const;
+  [[nodiscard]] bool ReadIntPtr(PickleIterator* iter, intptr_t* result) const;
+  [[nodiscard]] bool ReadUnsignedChar(PickleIterator* iter,
+                                      unsigned char* result) const;
+  [[nodiscard]] bool ReadString(PickleIterator* iter,
+                                std::string* result) const;
+  [[nodiscard]] bool ReadWString(PickleIterator* iter,
+                                 std::wstring* result) const;
+  [[nodiscard]] bool ReadBytesInto(PickleIterator* iter, void* data,
+                                   uint32_t length) const;
+  [[nodiscard]] bool ExtractBuffers(
       PickleIterator* iter, size_t length, BufferList* buffers,
       uint32_t alignment = sizeof(memberAlignmentType)) const;
 
   // Safer version of ReadInt() checks for the result not being negative.
   // Use it for reading the object sizes.
-  MOZ_MUST_USE bool ReadLength(PickleIterator* iter, int* result) const;
+  [[nodiscard]] bool ReadLength(PickleIterator* iter, int* result) const;
 
-  MOZ_MUST_USE bool ReadSentinel(PickleIterator* iter, uint32_t sentinel) const
+  [[nodiscard]] bool ReadSentinel(PickleIterator* iter, uint32_t sentinel) const
 #ifdef MOZ_PICKLE_SENTINEL_CHECKING
       ;
 #else
diff --git a/ipc/chromium/src/base/shared_memory.h b/ipc/chromium/src/base/shared_memory.h
index 8f7fa4e3b092..5762d8907670 100644
--- a/ipc/chromium/src/base/shared_memory.h
+++ b/ipc/chromium/src/base/shared_memory.h
@@ -122,7 +122,7 @@ class SharedMemory {
   //
   // (See bug 1479960 comment #0 for OS-specific implementation
   // details.)
-  MOZ_MUST_USE bool Freeze() {
+  [[nodiscard]] bool Freeze() {
     Unmap();
     return ReadOnlyCopy(this);
   }
@@ -141,7 +141,7 @@ class SharedMemory {
   // only if the memory was unmapped, but this is an implementation
   // detail and shouldn't be relied on; for that use case Freeze()
   // should be used instead.)
-  MOZ_MUST_USE bool ReadOnlyCopy(SharedMemory* ro_out);
+  [[nodiscard]] bool ReadOnlyCopy(SharedMemory* ro_out);
 
   // Closes the open shared memory segment.
   // It is safe to call Close repeatedly.
diff --git a/ipc/glue/IPCStreamUtils.h b/ipc/glue/IPCStreamUtils.h
index d30cd4738321..da854722478f 100644
--- a/ipc/glue/IPCStreamUtils.h
+++ b/ipc/glue/IPCStreamUtils.h
@@ -164,16 +164,16 @@ class AutoIPCStream {
   bool Serialize(nsIInputStream* aStream, net::SocketProcessChild* aManager);
 
   // Serialize the input stream.
-  MOZ_MUST_USE bool Serialize(nsIInputStream* aStream,
-                              dom::ContentParent* aManager);
+  [[nodiscard]] bool Serialize(nsIInputStream* aStream,
+                               dom::ContentParent* aManager);
 
   // Serialize the input stream.
-  MOZ_MUST_USE bool Serialize(nsIInputStream* aStream,
-                              PBackgroundParent* aManager);
+  [[nodiscard]] bool Serialize(nsIInputStream* aStream,
+                               PBackgroundParent* aManager);
 
   // Serialize the input stream.
-  MOZ_MUST_USE bool Serialize(nsIInputStream* aStream,
-                              net::SocketProcessParent* aManager);
+  [[nodiscard]] bool Serialize(nsIInputStream* aStream,
+                               net::SocketProcessParent* aManager);
 
   // Get the IPCStream as a non-optional value.  This will
   // assert if a stream has not been serialized or if it has already been taken.
diff --git a/ipc/glue/SharedMemory.h b/ipc/glue/SharedMemory.h
index 5f180f67be58..c7c230389e16 100644
--- a/ipc/glue/SharedMemory.h
+++ b/ipc/glue/SharedMemory.h
@@ -83,8 +83,8 @@ class SharedMemory {
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SharedMemory)
 
   static void SystemProtect(char* aAddr, size_t aSize, int aRights);
-  static MOZ_MUST_USE bool SystemProtectFallible(char* aAddr, size_t aSize,
-                                                 int aRights);
+  [[nodiscard]] static bool SystemProtectFallible(char* aAddr, size_t aSize,
+                                                  int aRights);
   static size_t SystemPageSize();
   static size_t PageAlignedSize(size_t aSize);
 
diff --git a/ipc/ipdl/ipdl/cxx/cgen.py b/ipc/ipdl/ipdl/cxx/cgen.py
index b87721124dfb..cc4391b463fe 100644
--- a/ipc/ipdl/ipdl/cxx/cgen.py
+++ b/ipc/ipdl/ipdl/cxx/cgen.py
@@ -218,7 +218,7 @@ class CxxCodeGen(CodePrinter, Visitor):
             self.printdent()
 
         if md.warn_unused:
-            self.write('MOZ_MUST_USE ')
+            self.write('[[nodiscard]] ')
 
         if md.methodspec == MethodSpec.STATIC:
             self.write('static ')
diff --git a/ipc/mscom/COMPtrHolder.h b/ipc/mscom/COMPtrHolder.h
index d817bac27a60..ee807e838c10 100644
--- a/ipc/mscom/COMPtrHolder.h
+++ b/ipc/mscom/COMPtrHolder.h
@@ -41,7 +41,7 @@ class COMPtrHolder {
 
   Interface* Get() const { return mPtr.get(); }
 
-  MOZ_MUST_USE Interface* Release() { return mPtr.release(); }
+  [[nodiscard]] Interface* Release() { return mPtr.release(); }
 
   void Set(COMPtrType&& aPtr) { mPtr = std::forward<COMPtrType>(aPtr); }