diff --git a/image/SurfaceCache.cpp b/image/SurfaceCache.cpp
index ca995ed8b1dd..439d38627eb1 100644
--- a/image/SurfaceCache.cpp
+++ b/image/SurfaceCache.cpp
@@ -270,7 +270,7 @@ class ImageSurfaceCache {
     return bytes;
   }
 
-  MOZ_MUST_USE bool Insert(NotNull<CachedSurface*> aSurface) {
+  [[nodiscard]] bool Insert(NotNull<CachedSurface*> aSurface) {
     MOZ_ASSERT(!mLocked || aSurface->IsPlaceholder() || aSurface->IsLocked(),
                "Inserting an unlocked surface for a locked image");
     return mSurfaces.Put(aSurface->GetSurfaceKey(),
diff --git a/image/decoders/icon/mac/nsIconChannel.h b/image/decoders/icon/mac/nsIconChannel.h
index 8c279310fa5d..dca2a3c51a49 100644
--- a/image/decoders/icon/mac/nsIconChannel.h
+++ b/image/decoders/icon/mac/nsIconChannel.h
@@ -49,8 +49,8 @@ class nsIconChannel final : public nsIChannel, public nsIStreamListener {
   nsCOMPtr<nsIStreamListener> mListener;
   bool mCanceled = false;
 
-  MOZ_MUST_USE nsresult MakeInputStream(nsIInputStream** _retval,
-                                        bool nonBlocking);
+  [[nodiscard]] nsresult MakeInputStream(nsIInputStream** _retval,
+                                         bool nonBlocking);
 
   nsresult ExtractIconInfoFromUrl(nsIFile** aLocalFile,
                                   uint32_t* aDesiredImageSize,
diff --git a/image/decoders/icon/nsIconURI.h b/image/decoders/icon/nsIconURI.h
index 7fa801a14f1e..94cb86253a37 100644
--- a/image/decoders/icon/nsIconURI.h
+++ b/image/decoders/icon/nsIconURI.h
@@ -84,7 +84,7 @@ class nsMozIconURI final : public nsIMozIconURI,
       return NS_ERROR_NOT_IMPLEMENTED;
     }
 
-    MOZ_MUST_USE NS_IMETHOD Read(nsIObjectInputStream* aStream) override {
+    [[nodiscard]] NS_IMETHOD Read(nsIObjectInputStream* aStream) override {
       return InitFromInputStream(aStream);
     }
 
diff --git a/image/decoders/icon/win/nsIconChannel.h b/image/decoders/icon/win/nsIconChannel.h
index 87c95f900153..f3bb93f3486f 100644
--- a/image/decoders/icon/win/nsIconChannel.h
+++ b/image/decoders/icon/win/nsIconChannel.h
@@ -69,8 +69,8 @@ class nsIconChannel final : public nsIChannel, public nsIStreamListener {
   nsresult GetHIconFromFile(bool aNonBlocking, HICON* hIcon);
   nsresult GetHIconFromFile(nsIFile* aLocalFile, const nsAutoString& aPath,
                             UINT aInfoFlags, HICON* hIcon);
-  MOZ_MUST_USE nsresult MakeInputStream(nsIInputStream** _retval,
-                                        bool aNonBlocking, HICON aIcon);
+  [[nodiscard]] nsresult MakeInputStream(nsIInputStream** _retval,
+                                         bool aNonBlocking, HICON aIcon);
 
   // Functions specific to Vista and above
  protected:
diff --git a/image/imgLoader.h b/image/imgLoader.h
index ea63a715f2a6..531fa2e74afe 100644
--- a/image/imgLoader.h
+++ b/image/imgLoader.h
@@ -239,7 +239,7 @@ class imgLoader final : public imgILoader,
   imgLoader();
   nsresult Init();
 
-  MOZ_MUST_USE nsresult LoadImage(
+  [[nodiscard]] nsresult LoadImage(
       nsIURI* aURI, nsIURI* aInitialDocumentURI, nsIReferrerInfo* aReferrerInfo,
       nsIPrincipal* aLoadingPrincipal, uint64_t aRequestContextID,
       nsILoadGroup* aLoadGroup, imgINotificationObserver* aObserver,
@@ -248,10 +248,10 @@ class imgLoader final : public imgILoader,
       nsContentPolicyType aContentPolicyType, const nsAString& initiatorType,
       bool aUseUrgentStartForChannel, imgRequestProxy** _retval);
 
-  MOZ_MUST_USE nsresult
-  LoadImageWithChannel(nsIChannel* channel, imgINotificationObserver* aObserver,
-                       nsISupports* aCX, nsIStreamListener** listener,
-                       imgRequestProxy** _retval);
+  [[nodiscard]] nsresult LoadImageWithChannel(
+      nsIChannel* channel, imgINotificationObserver* aObserver,
+      nsISupports* aCX, nsIStreamListener** listener,
+      imgRequestProxy** _retval);
 
   static nsresult GetMimeTypeFromContent(const char* aContents,
                                          uint32_t aLength,
diff --git a/image/imgRequest.h b/image/imgRequest.h
index 970561ccf3ef..3b0d12a398d0 100644
--- a/image/imgRequest.h
+++ b/image/imgRequest.h
@@ -62,12 +62,12 @@ class imgRequest final : public nsIStreamListener,
   NS_DECL_NSIINTERFACEREQUESTOR
   NS_DECL_NSIASYNCVERIFYREDIRECTCALLBACK
 
-  MOZ_MUST_USE nsresult Init(nsIURI* aURI, nsIURI* aFinalURI,
-                             bool aHadInsecureRedirect, nsIRequest* aRequest,
-                             nsIChannel* aChannel, imgCacheEntry* aCacheEntry,
-                             nsISupports* aCX,
-                             nsIPrincipal* aTriggeringPrincipal,
-                             int32_t aCORSMode, nsIReferrerInfo* aReferrerInfo);
+      [[nodiscard]] nsresult
+      Init(nsIURI* aURI, nsIURI* aFinalURI, bool aHadInsecureRedirect,
+           nsIRequest* aRequest, nsIChannel* aChannel,
+           imgCacheEntry* aCacheEntry, nsISupports* aCX,
+           nsIPrincipal* aTriggeringPrincipal, int32_t aCORSMode,
+           nsIReferrerInfo* aReferrerInfo);
 
   void ClearLoader();