diff --git a/dom/network/TCPSocketChild.cpp b/dom/network/TCPSocketChild.cpp
index e93b448db26..2de5ecfbe84 100644
--- a/dom/network/TCPSocketChild.cpp
+++ b/dom/network/TCPSocketChild.cpp
@@ -34,7 +34,9 @@ DeserializeArrayBuffer(JSContext* cx,
   JSObject* obj = JS_NewArrayBufferWithContents(cx, aBuffer.Length(), data.get());
   if (!obj)
       return false;
-  data.release();
+  // If JS_NewArrayBufferWithContents returns non-null, the ownership of
+  // the data is transfered to obj, so we release the ownership here.
+  mozilla::Unused << data.release();
 
   aVal.setObject(*obj);
   return true;
diff --git a/dom/workers/FileReaderSync.cpp b/dom/workers/FileReaderSync.cpp
index 5bd8e0122e4..4620544e483 100644
--- a/dom/workers/FileReaderSync.cpp
+++ b/dom/workers/FileReaderSync.cpp
@@ -7,6 +7,7 @@
 #include "FileReaderSync.h"
 
 #include "jsfriendapi.h"
+#include "mozilla/unused.h"
 #include "mozilla/Base64.h"
 #include "mozilla/dom/EncodingUtils.h"
 #include "mozilla/dom/File.h"
@@ -85,7 +86,9 @@ FileReaderSync::ReadAsArrayBuffer(JSContext* aCx,
     aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
     return;
   }
-  bufferData.release();
+  // arrayBuffer takes the ownership when it is not null. Otherwise we
+  // need to release it explicitly.
+  mozilla::Unused << bufferData.release();
 
   aRetval.set(arrayBuffer);
 }
diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index 71b31b11c0e..59e702d3ba7 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -7,6 +7,7 @@
 #include "builtin/TestingFunctions.h"
 
 #include "mozilla/Move.h"
+#include "mozilla/unused.h"
 
 #include <cmath>
 
@@ -2612,7 +2613,7 @@ FindPath(JSContext* cx, unsigned argc, Value* vp)
         RootedString edgeStr(cx, NewString<CanGC>(cx, edgeName.get(), js_strlen(edgeName.get())));
         if (!edgeStr)
             return false;
-        edgeName.release(); // edgeStr acquired ownership
+        mozilla::Unused << edgeName.release(); // edgeStr acquired ownership
 
         if (!JS_DefineProperty(cx, obj, "edge", edgeStr, JSPROP_ENUMERATE, nullptr, nullptr))
             return false;
diff --git a/js/src/jsstr.cpp b/js/src/jsstr.cpp
index 2f27187670e..f100561851b 100644
--- a/js/src/jsstr.cpp
+++ b/js/src/jsstr.cpp
@@ -13,6 +13,7 @@
 #include "mozilla/PodOperations.h"
 #include "mozilla/Range.h"
 #include "mozilla/TypeTraits.h"
+#include "mozilla/unused.h"
 
 #include <ctype.h>
 #include <string.h>
@@ -645,7 +646,7 @@ ToLowerCase(JSContext* cx, JSLinearString* str)
     if (!res)
         return nullptr;
 
-    newChars.release();
+    mozilla::Unused << newChars.release();
     return res;
 }
 
@@ -788,13 +789,13 @@ ToUpperCase(JSContext* cx, JSLinearString* str)
         if (!res)
             return nullptr;
 
-        newChars.ref<Latin1CharPtr>().release();
+        mozilla::Unused << newChars.ref<Latin1CharPtr>().release();
     } else {
         res = NewStringDontDeflate<CanGC>(cx, newChars.ref<TwoByteCharPtr>().get(), length);
         if (!res)
             return nullptr;
 
-        newChars.ref<TwoByteCharPtr>().release();
+        mozilla::Unused << newChars.ref<TwoByteCharPtr>().release();
     }
 
     return res;