--- a/netwerk/protocol/file/nsFileChannel.h
+++ b/netwerk/protocol/file/nsFileChannel.h
@@ -24,20 +24,22 @@ public:
 
 protected:
   ~nsFileChannel();
 
   // Called to construct a blocking file input stream for the given file.  This
   // method also returns a best guess at the content-type for the data stream.
   // NOTE: If the channel has a type hint set, contentType will be left
   // untouched. The caller should not use it in that case.
-  nsresult MakeFileInputStream(nsIFile *file, nsCOMPtr<nsIInputStream> &stream,
-                               nsCString &contentType, bool async);
+  MOZ_MUST_USE nsresult MakeFileInputStream(nsIFile *file,
+                                            nsCOMPtr<nsIInputStream> &stream,
+                                            nsCString &contentType, bool async);
 
-  virtual nsresult OpenContentStream(bool async, nsIInputStream **result,
-                                     nsIChannel** channel) override;
+  virtual MOZ_MUST_USE nsresult OpenContentStream(bool async,
+                                                  nsIInputStream **result,
+                                                  nsIChannel** channel) override;
 
 private:
   nsCOMPtr<nsIInputStream> mUploadStream;
   int64_t mUploadLength;
 };
 
 #endif // !nsFileChannel_h__

--- a/netwerk/protocol/file/nsFileProtocolHandler.h
+++ b/netwerk/protocol/file/nsFileProtocolHandler.h
@@ -16,12 +16,12 @@ class nsFileProtocolHandler : public nsI
 
 public:
     NS_DECL_THREADSAFE_ISUPPORTS
     NS_DECL_NSIPROTOCOLHANDLER
     NS_DECL_NSIFILEPROTOCOLHANDLER
 
     nsFileProtocolHandler();
 
-    nsresult Init();
+    MOZ_MUST_USE nsresult Init();
 };
 
 #endif // !nsFileProtocolHandler_h__