diff --git a/dom/media/MediaDecoderStateMachine.cpp b/dom/media/MediaDecoderStateMachine.cpp
index 5b5506504..b7053e847 100644
--- a/dom/media/MediaDecoderStateMachine.cpp
+++ b/dom/media/MediaDecoderStateMachine.cpp
@@ -1185,7 +1185,7 @@ void MediaDecoderStateMachine::MaybeStartPlayback()
   MOZ_ASSERT(mState == DECODER_STATE_DECODING ||
              mState == DECODER_STATE_COMPLETED);
 
-  if (IsPlaying()) {
+  if (MOZ_LIKELY(IsPlaying())) {
     // Logging this case is really spammy - don't do it.
     return;
   }
@@ -2443,7 +2443,7 @@ nsresult MediaDecoderStateMachine::RunStateMachine()
     }
 
     case DECODER_STATE_DECODING: {
-      if (IsDecodingFirstFrame()) {
+      if (MOZ_UNLIKELY(IsDecodingFirstFrame())) {
         // We haven't completed decoding our first frames, we can't start
         // playback yet.
         return NS_OK;
@@ -2623,7 +2623,7 @@ MediaDecoderStateMachine::CheckFrameValidity(VideoData* aData)
   MOZ_ASSERT(OnTaskQueue());
 
   // Update corrupt-frames statistics
-  if (aData->mImage && !aData->mImage->IsValid()) {
+  if (aData->mImage && MOZ_UNLIKELY(!aData->mImage->IsValid())) {
     FrameStatistics& frameStats = *mFrameStats;
     frameStats.NotifyCorruptFrame();
     // If more than 10% of the last 30 frames have been corrupted, then try disabling
@@ -2792,7 +2792,7 @@ MediaDecoderStateMachine::DropAudioUpToSeekTarget(MediaData* aSample)
          audio->mAudioData.get() + (framesToPrune.value() * channels),
          frames * channels * sizeof(AudioDataValue));
   CheckedInt64 duration = FramesToUsecs(frames, mInfo.mAudio.mRate);
-  if (!duration.isValid()) {
+  if (MOZ_UNLIKELY(!duration.isValid())) {
     return NS_ERROR_FAILURE;
   }
   RefPtr<AudioData> data(new AudioData(audio->mOffset,
diff --git a/dom/media/webm/SoftwareWebMVideoDecoder.cpp b/dom/media/webm/SoftwareWebMVideoDecoder.cpp
index d63e24c73..fef42b410 100644
--- a/dom/media/webm/SoftwareWebMVideoDecoder.cpp
+++ b/dom/media/webm/SoftwareWebMVideoDecoder.cpp
@@ -88,24 +88,24 @@ SoftwareWebMVideoDecoder::DecodeVideoFrame(bool &aKeyframeSkip,
   AbstractMediaDecoder::AutoNotifyDecoded a(mReader->GetDecoder());
 
   RefPtr<NesteggPacketHolder> holder(mReader->NextPacket(WebMReader::VIDEO));
-  if (!holder) {
+  if (MOZ_UNLIKELY(!holder)) {
     return false;
   }
 
   nestegg_packet* packet = holder->Packet();
   unsigned int track = 0;
   int r = nestegg_packet_track(packet, &track);
-  if (r == -1) {
+  if (MOZ_UNLIKELY(r == -1)) {
     return false;
   }
 
   unsigned int count = 0;
   r = nestegg_packet_count(packet, &count);
-  if (r == -1) {
+  if (MOZ_UNLIKELY(r == -1)) {
     return false;
   }
 
-  if (count > 1) {
+  if (MOZ_UNLIKELY(count > 1)) {
     NS_WARNING("Packet contains more than one video frame");
     return false;
   }
@@ -130,7 +130,7 @@ SoftwareWebMVideoDecoder::DecodeVideoFrame(bool &aKeyframeSkip,
   unsigned char* data;
   size_t length;
   r = nestegg_packet_data(packet, 0, &data, &length);
-  if (r == -1) {
+  if (MOZ_UNLIKELY(r == -1)) {
     return false;
   }
 
@@ -153,7 +153,7 @@ SoftwareWebMVideoDecoder::DecodeVideoFrame(bool &aKeyframeSkip,
     aKeyframeSkip = false;
   }
 
-  if (vpx_codec_decode(&mVPX, data, length, nullptr, 0)) {
+  if (MOZ_UNLIKELY(vpx_codec_decode(&mVPX, data, length, nullptr, 0))) {
     return false;
   }
 
@@ -217,7 +217,7 @@ SoftwareWebMVideoDecoder::DecodeVideoFrame(bool &aKeyframeSkip,
                                               si.is_kf,
                                               -1,
                                               picture);
-    if (!v) {
+    if (MOZ_UNLIKELY(!v)) {
       return false;
     }
     a.mParsed++;
diff --git a/dom/media/webm/WebMReader.cpp b/dom/media/webm/WebMReader.cpp
index 41c3a4381..01d7267cb 100644
--- a/dom/media/webm/WebMReader.cpp
+++ b/dom/media/webm/WebMReader.cpp
@@ -417,7 +417,7 @@ bool WebMReader::DecodeAudioPacket(NesteggPacketHolder* aHolder)
   int r = 0;
   unsigned int count = 0;
   r = nestegg_packet_count(aHolder->Packet(), &count);
-  if (r == -1) {
+  if (MOZ_UNLIKELY(r == -1)) {
     return false;
   }
 
@@ -439,7 +439,7 @@ bool WebMReader::DecodeAudioPacket(NesteggPacketHolder* aHolder)
     return false;
   }
   decoded_frames += mAudioFrames;
-  if (!decoded_frames.isValid()) {
+  if (MOZ_UNLIKELY(!decoded_frames.isValid())) {
     NS_WARNING("Int overflow adding decoded_frames");
     return false;
   }
@@ -460,7 +460,7 @@ bool WebMReader::DecodeAudioPacket(NesteggPacketHolder* aHolder)
     unsigned char* data;
     size_t length;
     r = nestegg_packet_data(aHolder->Packet(), i, &data, &length);
-    if (r == -1) {
+    if (MOZ_UNLIKELY(r == -1)) {
       return false;
     }
     int64_t discardPadding = 0;
@@ -508,7 +508,7 @@ RefPtr<NesteggPacketHolder> WebMReader::NextPacket(TrackType aTrackType)
 
   do {
     RefPtr<NesteggPacketHolder> holder = DemuxPacket();
-    if (!holder) {
+    if (MOZ_UNLIKELY(!holder)) {
       return nullptr;
     }
 
@@ -530,13 +530,13 @@ WebMReader::DemuxPacket()
 {
   nestegg_packet* packet;
   int r = nestegg_read_packet(mContext, &packet);
-  if (r <= 0) {
+  if (MOZ_UNLIKELY(r <= 0)) {
     return nullptr;
   }
 
   unsigned int track = 0;
   r = nestegg_packet_track(packet, &track);
-  if (r == -1) {
+  if (MOZ_UNLIKELY(r == -1)) {
     return nullptr;
   }
 
@@ -548,7 +548,7 @@ WebMReader::DemuxPacket()
     unsigned char* data;
     size_t length;
     r = nestegg_packet_data(packet, 0, &data, &length);
-    if (r == -1) {
+    if (MOZ_UNLIKELY(r == -1)) {
       return nullptr;
     }
     vpx_codec_stream_info_t si;
@@ -576,7 +576,7 @@ bool WebMReader::DecodeAudioData()
   MOZ_ASSERT(OnTaskQueue());
 
   RefPtr<NesteggPacketHolder> holder(NextPacket(AUDIO));
-  if (!holder) {
+  if (MOZ_UNLIKELY(!holder)) {
     return false;
   }
 
@@ -589,7 +589,7 @@ bool WebMReader::FilterPacketByTime(int64_t aEndTime, WebMPacketQueue& aOutput)
   // than aEndTime.
   while (true) {
     RefPtr<NesteggPacketHolder> holder(NextPacket(VIDEO));
-    if (!holder) {
+    if (MOZ_UNLIKELY(!holder)) {
       break;
     }
     int64_t tstamp = holder->Timestamp();
@@ -622,7 +622,7 @@ int64_t WebMReader::GetNextKeyframeTime(int64_t aTimeThreshold)
   int64_t keyframeTime = -1;
   while (!foundKeyframe) {
     RefPtr<NesteggPacketHolder> holder(NextPacket(VIDEO));
-    if (!holder) {
+    if (MOZ_UNLIKELY(!holder)) {
       break;
     }