diff --git a/image/DecodePool.cpp b/image/DecodePool.cpp
index 5101451c11f9..9aa3d58229f4 100644
--- a/image/DecodePool.cpp
+++ b/image/DecodePool.cpp
@@ -328,7 +328,7 @@ DecodePool::AsyncRun(IDecodingTask* aTask)
   mImpl->PushWork(aTask);
 }
 
-void
+bool
 DecodePool::SyncRunIfPreferred(IDecodingTask* aTask)
 {
   MOZ_ASSERT(NS_IsMainThread());
@@ -336,10 +336,11 @@ DecodePool::SyncRunIfPreferred(IDecodingTask* aTask)
 
   if (aTask->ShouldPreferSyncRun()) {
     aTask->Run();
-    return;
+    return true;
   }
 
   AsyncRun(aTask);
+  return false;
 }
 
 void
diff --git a/image/DecodePool.h b/image/DecodePool.h
index 9d62731e500f..e8823d4f0118 100644
--- a/image/DecodePool.h
+++ b/image/DecodePool.h
@@ -62,8 +62,9 @@ public:
    * itself to make this decision; @see IDecodingTask::ShouldPreferSyncRun(). If
    * @aTask doesn't prefer it, just run @aTask asynchronously and return
    * immediately.
+   * @return true if the task was run sync, false otherwise.
    */
-  void SyncRunIfPreferred(IDecodingTask* aTask);
+  bool SyncRunIfPreferred(IDecodingTask* aTask);
 
   /**
    * Run @aTask synchronously. This does not guarantee that @aTask will complete
diff --git a/image/RasterImage.cpp b/image/RasterImage.cpp
index ed5624d42c70..edeac73fb7b7 100644
--- a/image/RasterImage.cpp
+++ b/image/RasterImage.cpp
@@ -336,10 +336,10 @@ RasterImage::LookupFrame(const IntSize& aSize,
                !mAnimationState || mAnimationState->KnownFrameCount() < 1,
                "Animated frames should be locked");
 
-    Decode(requestedSize, aFlags, aPlaybackType);
+    bool ranSync = Decode(requestedSize, aFlags, aPlaybackType);
 
-    // If we can sync decode, we should already have the frame.
-    if (aFlags & FLAG_SYNC_DECODE) {
+    // If we can or did sync decode, we should already have the frame.
+    if (ranSync || (aFlags & FLAG_SYNC_DECODE)) {
       result = LookupFrameInternal(requestedSize, aFlags, aPlaybackType);
     }
   }
@@ -1080,7 +1080,7 @@ RasterImage::RequestDecodeForSize(const IntSize& aSize, uint32_t aFlags)
   return NS_OK;
 }
 
-static void
+static bool
 LaunchDecodingTask(IDecodingTask* aTask,
                    RasterImage* aImage,
                    uint32_t aFlags,
@@ -1093,24 +1093,24 @@ LaunchDecodingTask(IDecodingTask* aTask,
         js::ProfileEntry::Category::GRAPHICS,
         "%s", aImage->GetURIString().get());
       DecodePool::Singleton()->SyncRunIfPossible(aTask);
-      return;
+      return true;
     }
 
     if (aFlags & imgIContainer::FLAG_SYNC_DECODE_IF_FAST) {
       PROFILER_LABEL_PRINTF("DecodePool", "SyncRunIfPreferred",
         js::ProfileEntry::Category::GRAPHICS,
         "%s", aImage->GetURIString().get());
-      DecodePool::Singleton()->SyncRunIfPreferred(aTask);
-      return;
+      return DecodePool::Singleton()->SyncRunIfPreferred(aTask);
     }
   }
 
   // Perform an async decode. We also take this path if we don't have all the
   // source data yet, since sync decoding is impossible in that situation.
   DecodePool::Singleton()->AsyncRun(aTask);
+  return false;
 }
 
-NS_IMETHODIMP
+bool
 RasterImage::Decode(const IntSize& aSize,
                     uint32_t aFlags,
                     PlaybackType aPlaybackType)
@@ -1118,13 +1118,13 @@ RasterImage::Decode(const IntSize& aSize,
   MOZ_ASSERT(NS_IsMainThread());
 
   if (mError) {
-    return NS_ERROR_FAILURE;
+    return false;
   }
 
   // If we don't have a size yet, we can't do any other decoding.
   if (!mHasSize) {
     mWantFullDecode = true;
-    return NS_OK;
+    return false;
   }
 
   // We're about to decode again, which may mean that some of the previous sizes
@@ -1169,14 +1169,13 @@ RasterImage::Decode(const IntSize& aSize,
 
   // Make sure DecoderFactory was able to create a decoder successfully.
   if (!task) {
-    return NS_ERROR_FAILURE;
+    return false;
   }
 
   mDecodeCount++;
 
   // We're ready to decode; start the decoder.
-  LaunchDecodingTask(task, this, aFlags, mHasSourceData);
-  return NS_OK;
+  return LaunchDecodingTask(task, this, aFlags, mHasSourceData);
 }
 
 NS_IMETHODIMP
diff --git a/image/RasterImage.h b/image/RasterImage.h
index 9fe86fde3ffa..bc80e77c258d 100644
--- a/image/RasterImage.h
+++ b/image/RasterImage.h
@@ -336,10 +336,12 @@ private:
    *
    * It's an error to call Decode() before this image's intrinsic size is
    * available. A metadata decode must successfully complete first.
+   *
+   * Returns true of the decode was run synchronously.
    */
-  NS_IMETHOD Decode(const gfx::IntSize& aSize,
-                    uint32_t aFlags,
-                    PlaybackType aPlaybackType);
+  bool Decode(const gfx::IntSize& aSize,
+              uint32_t aFlags,
+              PlaybackType aPlaybackType);
 
   /**
    * Creates and runs a metadata decoder, either synchronously or