--- a/dom/media/DecoderTraits.cpp
+++ b/dom/media/DecoderTraits.cpp
@@ -353,17 +353,17 @@ DecoderTraits::CreateReader(const MediaC
 
 #ifdef MOZ_FMP4
   if (MP4Decoder::IsSupportedType(aType,
                                   /* DecoderDoctorDiagnostics* */ nullptr)) {
     decoderReader = new MediaFormatReader(aDecoder, new MP4Demuxer(aDecoder->GetResource()));
   } else
 #endif
   if (MP3Decoder::IsSupportedType(aType)) {
-    decoderReader = new MediaFormatReader(aDecoder, new mp3::MP3Demuxer(aDecoder->GetResource()));
+    decoderReader = new MediaFormatReader(aDecoder, new MP3Demuxer(aDecoder->GetResource()));
   } else
   if (ADTSDecoder::IsSupportedType(aType)) {
     decoderReader = new MediaFormatReader(aDecoder, new ADTSDemuxer(aDecoder->GetResource()));
   } else
   if (WaveDecoder::IsSupportedType(aType)) {
     decoderReader = new MediaFormatReader(aDecoder, new WAVDemuxer(aDecoder->GetResource()));
   } else
   if (FlacDecoder::IsSupportedType(aType)) {

--- a/dom/media/gtest/TestMP3Demuxer.cpp
+++ b/dom/media/gtest/TestMP3Demuxer.cpp
@@ -6,17 +6,16 @@
 #include <gtest/gtest.h>
 #include <vector>
 
 #include "MP3Demuxer.h"
 #include "mozilla/ArrayUtils.h"
 #include "MockMediaResource.h"
 
 using namespace mozilla;
-using namespace mozilla::mp3;
 using media::TimeUnit;
 
 
 // Regular MP3 file mock resource.
 class MockMP3MediaResource : public MockMediaResource {
 public:
   explicit MockMP3MediaResource(const char* aFileName)
     : MockMediaResource(aFileName)

--- a/dom/media/mp3/MP3Decoder.cpp
+++ b/dom/media/mp3/MP3Decoder.cpp
@@ -21,17 +21,17 @@ MP3Decoder::Clone(MediaDecoderInit& aIni
     return nullptr;
   }
   return new MP3Decoder(aInit);
 }
 
 MediaDecoderStateMachine*
 MP3Decoder::CreateStateMachine() {
   RefPtr<MediaDecoderReader> reader =
-      new MediaFormatReader(this, new mp3::MP3Demuxer(GetResource()));
+      new MediaFormatReader(this, new MP3Demuxer(GetResource()));
   return new MediaDecoderStateMachine(this, reader);
 }
 
 /* static */
 bool
 MP3Decoder::IsEnabled() {
   RefPtr<PDMFactory> platform = new PDMFactory();
   return platform->SupportsMimeType(NS_LITERAL_CSTRING("audio/mpeg"),

--- a/dom/media/mp3/MP3Demuxer.cpp
+++ b/dom/media/mp3/MP3Demuxer.cpp
@@ -23,17 +23,16 @@ extern mozilla::LazyLogModule gMediaDemu
   MOZ_LOG(gMediaDemuxerLog, LogLevel::Verbose, ("MP3Demuxer " msg, ##__VA_ARGS__))
 
 using mozilla::media::TimeUnit;
 using mozilla::media::TimeInterval;
 using mozilla::media::TimeIntervals;
 using mp4_demuxer::ByteReader;
 
 namespace mozilla {
-namespace mp3 {
 
 // MP3Demuxer
 
 MP3Demuxer::MP3Demuxer(MediaResource* aSource) : mSource(aSource) { }
 
 bool
 MP3Demuxer::InitInternal()
 {
@@ -769,10 +768,9 @@ MP3TrackDemuxer::AverageFrameLength() co
   const auto& vbr = mParser.VBRInfo();
   if (vbr.IsComplete() && vbr.NumAudioFrames().value() + 1) {
     return static_cast<double>(vbr.NumBytes().value())
            / (vbr.NumAudioFrames().value() + 1);
   }
   return 0.0;
 }
 
-} // namespace mp3
 } // namespace mozilla

--- a/dom/media/mp3/MP3Demuxer.h
+++ b/dom/media/mp3/MP3Demuxer.h
@@ -5,17 +5,16 @@
 #ifndef MP3_DEMUXER_H_
 #define MP3_DEMUXER_H_
 
 #include "MediaDataDemuxer.h"
 #include "MediaResource.h"
 #include "MP3FrameParser.h"
 
 namespace mozilla {
-namespace mp3 {
 
 class MP3TrackDemuxer;
 
 class MP3Demuxer : public MediaDataDemuxer
 {
 public:
   // MediaDataDemuxer interface.
   explicit MP3Demuxer(MediaResource* aSource);
@@ -152,12 +151,11 @@ private:
 
   // Channel count derived from frame headers or 0 if none available.
   int32_t mChannels;
 
   // Audio track config info.
   UniquePtr<AudioInfo> mInfo;
 };
 
-} // namespace mp3
 } // namespace mozilla
 
 #endif

--- a/dom/media/mp3/MP3FrameParser.cpp
+++ b/dom/media/mp3/MP3FrameParser.cpp
@@ -18,17 +18,16 @@ extern mozilla::LazyLogModule gMediaDemu
 #define MP3LOG(msg, ...) \
   MOZ_LOG(gMediaDemuxerLog, LogLevel::Debug, ("MP3Demuxer " msg, ##__VA_ARGS__))
 #define MP3LOGV(msg, ...) \
   MOZ_LOG(gMediaDemuxerLog, LogLevel::Verbose, ("MP3Demuxer " msg, ##__VA_ARGS__))
 
 using mp4_demuxer::ByteReader;
 
 namespace mozilla {
-namespace mp3 {
 
 // FrameParser
 
 namespace frame_header {
 // FrameHeader mRaw byte offsets.
 static const int SYNC1 = 0;
 static const int SYNC2_VERSION_LAYER_PROTECTION = 1;
 static const int BITRATE_SAMPLERATE_PADDING_PRIVATE = 2;
@@ -729,10 +728,9 @@ ID3Parser::ID3Header::Update(uint8_t c)
     mSize |= c;
   }
   if (mPos < SIZE) {
     mRaw[mPos] = c;
   }
   return IsValid(mPos++);
 }
 
-} // namespace mp3
 } // namespace mozilla

--- a/dom/media/mp3/MP3FrameParser.h
+++ b/dom/media/mp3/MP3FrameParser.h
@@ -6,17 +6,16 @@
 #define MP3_FRAME_PARSER_H_
 
 #include <vector>
 
 #include "mozilla/Maybe.h"
 #include "mp4_demuxer/ByteReader.h"
 
 namespace mozilla {
-namespace mp3 {
 
 // ID3 header parser state machine used by FrameParser.
 // The header contains the following format (one byte per term):
 // 'I' 'D' '3' MajorVersion MinorVersion Flags Size1 Size2 Size3 Size4
 // For more details see http://id3.org/id3v2.3.0.
 class ID3Parser
 {
 public:
@@ -333,12 +332,11 @@ private:
 
   // We keep the first parsed frame around for static info access, the
   // previously parsed frame for debugging and the currently parsed frame.
   Frame mFirstFrame;
   Frame mFrame;
   Frame mPrevFrame;
 };
 
-} // namespace mp3
 } // namespace mozilla
 
 #endif