diff --git a/dom/media/mediasource/AutoTaskQueue.h b/dom/media/mediasource/AutoTaskQueue.h
index c3aa08291a70..38432a01e4ce 100644
--- a/dom/media/mediasource/AutoTaskQueue.h
+++ b/dom/media/mediasource/AutoTaskQueue.h
@@ -36,11 +36,11 @@ public:
     return mTaskQueue->TailDispatcher();
   }
 
-  void Dispatch(already_AddRefed<nsIRunnable> aRunnable,
-                DispatchFailureHandling aFailureHandling = AssertDispatchSuccess,
-                DispatchReason aReason = NormalDispatch) override
+  nsresult Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                    DispatchFailureHandling aFailureHandling = AssertDispatchSuccess,
+                    DispatchReason aReason = NormalDispatch) override
   {
-    mTaskQueue->Dispatch(Move(aRunnable), aFailureHandling, aReason);
+    return mTaskQueue->Dispatch(Move(aRunnable), aFailureHandling, aReason);
   }
 
   // Prevent a GCC warning about the other overload of Dispatch being hidden.
diff --git a/xpcom/threads/AbstractThread.cpp b/xpcom/threads/AbstractThread.cpp
index bcae3882fc0a..d8b65c8bbb77 100644
--- a/xpcom/threads/AbstractThread.cpp
+++ b/xpcom/threads/AbstractThread.cpp
@@ -46,20 +46,20 @@ public:
     MOZ_ASSERT_IF(aRequireTailDispatch, NS_IsMainThread() && aTarget->IsOnCurrentThread());
   }
 
-  virtual void Dispatch(already_AddRefed<nsIRunnable> aRunnable,
-                        DispatchFailureHandling aFailureHandling = AssertDispatchSuccess,
-                        DispatchReason aReason = NormalDispatch) override
+  virtual nsresult Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                            DispatchFailureHandling aFailureHandling = AssertDispatchSuccess,
+                            DispatchReason aReason = NormalDispatch) override
   {
     AbstractThread* currentThread;
     if (aReason != TailDispatch && (currentThread = GetCurrent()) && RequiresTailDispatch(currentThread)) {
       currentThread->TailDispatcher().AddTask(this, Move(aRunnable), aFailureHandling);
-      return;
+      return NS_OK;
     }
 
     RefPtr<nsIRunnable> runner(new Runner(this, Move(aRunnable), false /* already drained by TaskGroupRunnable  */));
     nsresult rv = mTarget->Dispatch(runner.forget(), NS_DISPATCH_NORMAL);
     MOZ_DIAGNOSTIC_ASSERT(aFailureHandling == DontAssertDispatchSuccess || NS_SUCCEEDED(rv));
-    Unused << rv;
+    return rv;
   }
 
   // Prevent a GCC warning about the other overload of Dispatch being hidden.
diff --git a/xpcom/threads/AbstractThread.h b/xpcom/threads/AbstractThread.h
index cb4a1a37a985..60b329c490a9 100644
--- a/xpcom/threads/AbstractThread.h
+++ b/xpcom/threads/AbstractThread.h
@@ -69,9 +69,9 @@ public:
 
   enum DispatchFailureHandling { AssertDispatchSuccess, DontAssertDispatchSuccess };
   enum DispatchReason { NormalDispatch, TailDispatch };
-  virtual void Dispatch(already_AddRefed<nsIRunnable> aRunnable,
-                        DispatchFailureHandling aHandling = AssertDispatchSuccess,
-                        DispatchReason aReason = NormalDispatch) = 0;
+  virtual nsresult Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                            DispatchFailureHandling aHandling = AssertDispatchSuccess,
+                            DispatchReason aReason = NormalDispatch) = 0;
 
   virtual bool IsCurrentThreadIn() = 0;
 
diff --git a/xpcom/threads/TaskQueue.h b/xpcom/threads/TaskQueue.h
index b97586c8eccb..032a9b2d0a2a 100644
--- a/xpcom/threads/TaskQueue.h
+++ b/xpcom/threads/TaskQueue.h
@@ -61,9 +61,9 @@ public:
 
   TaskQueue* AsTaskQueue() override { return this; }
 
-  void Dispatch(already_AddRefed<nsIRunnable> aRunnable,
-                DispatchFailureHandling aFailureHandling = AssertDispatchSuccess,
-                DispatchReason aReason = NormalDispatch) override
+  nsresult Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                    DispatchFailureHandling aFailureHandling = AssertDispatchSuccess,
+                    DispatchReason aReason = NormalDispatch) override
   {
     nsCOMPtr<nsIRunnable> r = aRunnable;
     {
@@ -74,7 +74,7 @@ public:
         MOZ_CRASH_UNSAFE_PRINTF("%s: Dispatch failed. rv=%x", mName, uint32_t(rv));
       }
 #endif
-      Unused << rv;
+      return rv;
     }
     // If the ownership of |r| is not transferred in DispatchLocked() due to
     // dispatch failure, it will be deleted here outside the lock. We do so