--- a/dom/media/platforms/PDMFactory.cpp
+++ b/dom/media/platforms/PDMFactory.cpp
@@ -222,17 +222,17 @@ PDMFactory::CreateDecoderWithPDM(Platfor
   if (callbackWrapper && m) {
     m = new DecoderFuzzingWrapper(m.forget(), callbackWrapper.forget());
   }
 
   return m.forget();
 }
 
 bool
-PDMFactory::SupportsMimeType(const nsACString& aMimeType)
+PDMFactory::SupportsMimeType(const nsACString& aMimeType) const
 {
   if (mEMEPDM) {
     return mEMEPDM->SupportsMimeType(aMimeType);
   }
   RefPtr<PlatformDecoderModule> current = GetDecoder(aMimeType);
   return !!current;
 }
 
@@ -300,17 +300,17 @@ PDMFactory::StartupPDM(PlatformDecoderMo
   if (aPDM && NS_SUCCEEDED(aPDM->Startup())) {
     mCurrentPDMs.AppendElement(aPDM);
     return true;
   }
   return false;
 }
 
 already_AddRefed<PlatformDecoderModule>
-PDMFactory::GetDecoder(const nsACString& aMimeType)
+PDMFactory::GetDecoder(const nsACString& aMimeType) const
 {
   RefPtr<PlatformDecoderModule> pdm;
   for (auto& current : mCurrentPDMs) {
     if (current->SupportsMimeType(aMimeType)) {
       pdm = current;
       break;
     }
   }

--- a/dom/media/platforms/PDMFactory.h
+++ b/dom/media/platforms/PDMFactory.h
@@ -30,34 +30,36 @@ public:
   // This is called on the decode task queue.
   already_AddRefed<MediaDataDecoder>
   CreateDecoder(const TrackInfo& aConfig,
                 FlushableTaskQueue* aTaskQueue,
                 MediaDataDecoderCallback* aCallback,
                 layers::LayersBackend aLayersBackend = layers::LayersBackend::LAYERS_NONE,
                 layers::ImageContainer* aImageContainer = nullptr);
 
-  bool SupportsMimeType(const nsACString& aMimeType);
+  bool SupportsMimeType(const nsACString& aMimeType) const;
 
 #ifdef MOZ_EME
   // Creates a PlatformDecoderModule that uses a CDMProxy to decrypt or
   // decrypt-and-decode EME encrypted content. If the CDM only decrypts and
   // does not decode, we create a PDM and use that to create MediaDataDecoders
   // that we use on on aTaskQueue to decode the decrypted stream.
   // This is called on the decode task queue.
   void SetCDMProxy(CDMProxy* aProxy);
 #endif
 
 private:
   virtual ~PDMFactory();
   void CreatePDMs();
   // Startup the provided PDM and add it to our list if successful.
   bool StartupPDM(PlatformDecoderModule* aPDM);
   // Returns the first PDM in our list supporting the mimetype.
-  already_AddRefed<PlatformDecoderModule> GetDecoder(const nsACString& aMimeType);
+  already_AddRefed<PlatformDecoderModule>
+  GetDecoder(const nsACString& aMimeType) const;
+
   already_AddRefed<MediaDataDecoder>
   CreateDecoderWithPDM(PlatformDecoderModule* aPDM,
                        const TrackInfo& aConfig,
                        FlushableTaskQueue* aTaskQueue,
                        MediaDataDecoderCallback* aCallback,
                        layers::LayersBackend aLayersBackend,
                        layers::ImageContainer* aImageContainer);
 

--- a/dom/media/platforms/agnostic/AgnosticDecoderModule.cpp
+++ b/dom/media/platforms/agnostic/AgnosticDecoderModule.cpp
@@ -7,17 +7,17 @@
 #include "AgnosticDecoderModule.h"
 #include "OpusDecoder.h"
 #include "VorbisDecoder.h"
 #include "VPXDecoder.h"
 
 namespace mozilla {
 
 bool
-AgnosticDecoderModule::SupportsMimeType(const nsACString& aMimeType)
+AgnosticDecoderModule::SupportsMimeType(const nsACString& aMimeType) const
 {
   return VPXDecoder::IsVPX(aMimeType) ||
     OpusDataDecoder::IsOpus(aMimeType) ||
     VorbisDataDecoder::IsVorbis(aMimeType);
 }
 
 already_AddRefed<MediaDataDecoder>
 AgnosticDecoderModule::CreateVideoDecoder(const VideoInfo& aConfig,

--- a/dom/media/platforms/agnostic/AgnosticDecoderModule.h
+++ b/dom/media/platforms/agnostic/AgnosticDecoderModule.h
@@ -5,17 +5,17 @@
 
 namespace mozilla {
 
 class AgnosticDecoderModule : public PlatformDecoderModule {
 public:
   AgnosticDecoderModule() = default;
   virtual ~AgnosticDecoderModule() = default;
 
-  bool SupportsMimeType(const nsACString& aMimeType) override;
+  bool SupportsMimeType(const nsACString& aMimeType) const override;
 
   ConversionRequired
   DecoderNeedsConversion(const TrackInfo& aConfig) const override
   {
     return ConversionRequired::kNeedNone;
   }
 
 protected:

--- a/dom/media/platforms/agnostic/BlankDecoderModule.cpp
+++ b/dom/media/platforms/agnostic/BlankDecoderModule.cpp
@@ -241,17 +241,17 @@ public:
       new BlankMediaDataDecoder<BlankAudioDataCreator>(creator,
                                                        aAudioTaskQueue,
                                                        aCallback,
                                                        TrackInfo::kAudioTrack);
     return decoder.forget();
   }
 
   bool
-  SupportsMimeType(const nsACString& aMimeType) override
+  SupportsMimeType(const nsACString& aMimeType) const override
   {
     return true;
   }
 
   ConversionRequired
   DecoderNeedsConversion(const TrackInfo& aConfig) const override
   {
     return kNeedNone;

--- a/dom/media/platforms/agnostic/eme/EMEDecoderModule.cpp
+++ b/dom/media/platforms/agnostic/eme/EMEDecoderModule.cpp
@@ -298,16 +298,16 @@ EMEDecoderModule::DecoderNeedsConversion
   if (aConfig.IsVideo()) {
     return kNeedAVCC;
   } else {
     return kNeedNone;
   }
 }
 
 bool
-EMEDecoderModule::SupportsMimeType(const nsACString& aMimeType)
+EMEDecoderModule::SupportsMimeType(const nsACString& aMimeType) const
 {
   Maybe<nsCString> gmp;
   gmp.emplace(NS_ConvertUTF16toUTF8(mProxy->KeySystem()));
   return GMPDecoderModule::SupportsMimeType(aMimeType, gmp);
 }
 
 } // namespace mozilla

--- a/dom/media/platforms/agnostic/eme/EMEDecoderModule.h
+++ b/dom/media/platforms/agnostic/eme/EMEDecoderModule.h
@@ -40,17 +40,17 @@ protected:
   CreateAudioDecoder(const AudioInfo& aConfig,
                      FlushableTaskQueue* aAudioTaskQueue,
                      MediaDataDecoderCallback* aCallback) override;
 
   ConversionRequired
   DecoderNeedsConversion(const TrackInfo& aConfig) const override;
 
   bool
-  SupportsMimeType(const nsACString& aMimeType) override;
+  SupportsMimeType(const nsACString& aMimeType) const override;
 
 private:
   RefPtr<CDMProxy> mProxy;
   // Will be null if CDM has decoding capability.
   RefPtr<PDMFactory> mPDM;
   // We run the PDM on its own task queue.
   RefPtr<TaskQueue> mTaskQueue;
   bool mCDMDecodesAudio;

--- a/dom/media/platforms/agnostic/gmp/GMPDecoderModule.cpp
+++ b/dom/media/platforms/agnostic/gmp/GMPDecoderModule.cpp
@@ -223,14 +223,14 @@ GMPDecoderModule::SupportsMimeType(const
       return true;
     }
   }
 
   return false;
 }
 
 bool
-GMPDecoderModule::SupportsMimeType(const nsACString& aMimeType)
+GMPDecoderModule::SupportsMimeType(const nsACString& aMimeType) const
 {
   return SupportsMimeType(aMimeType, PreferredGMP(aMimeType));
 }
 
 } // namespace mozilla

--- a/dom/media/platforms/agnostic/gmp/GMPDecoderModule.h
+++ b/dom/media/platforms/agnostic/gmp/GMPDecoderModule.h
@@ -31,17 +31,17 @@ public:
   CreateAudioDecoder(const AudioInfo& aConfig,
                      FlushableTaskQueue* aAudioTaskQueue,
                      MediaDataDecoderCallback* aCallback) override;
 
   ConversionRequired
   DecoderNeedsConversion(const TrackInfo& aConfig) const override;
 
   bool
-  SupportsMimeType(const nsACString& aMimeType) override;
+  SupportsMimeType(const nsACString& aMimeType) const override;
 
   // Main thread only.
   static void Init();
 
   static const Maybe<nsCString> PreferredGMP(const nsACString& aMimeType);
 
   static bool SupportsMimeType(const nsACString& aMimeType,
                                const Maybe<nsCString>& aGMP);

--- a/dom/media/platforms/android/AndroidDecoderModule.h
+++ b/dom/media/platforms/android/AndroidDecoderModule.h
@@ -31,17 +31,17 @@ public:
   CreateAudioDecoder(const AudioInfo& aConfig,
                      FlushableTaskQueue* aAudioTaskQueue,
                      MediaDataDecoderCallback* aCallback) override;
 
 
   AndroidDecoderModule() {}
   virtual ~AndroidDecoderModule() {}
 
-  bool SupportsMimeType(const nsACString& aMimeType) override;
+  bool SupportsMimeType(const nsACString& aMimeType) const override;
 
   ConversionRequired
   DecoderNeedsConversion(const TrackInfo& aConfig) const override;
 };
 
 class MediaCodecDataDecoder : public MediaDataDecoder {
 public:
 

--- a/dom/media/platforms/apple/AppleDecoderModule.cpp
+++ b/dom/media/platforms/apple/AppleDecoderModule.cpp
@@ -112,17 +112,17 @@ AppleDecoderModule::CreateAudioDecoder(c
                                        MediaDataDecoderCallback* aCallback)
 {
   RefPtr<MediaDataDecoder> decoder =
     new AppleATDecoder(aConfig, aAudioTaskQueue, aCallback);
   return decoder.forget();
 }
 
 bool
-AppleDecoderModule::SupportsMimeType(const nsACString& aMimeType)
+AppleDecoderModule::SupportsMimeType(const nsACString& aMimeType) const
 {
   return (sIsCoreMediaAvailable &&
           (aMimeType.EqualsLiteral("audio/mpeg") ||
            aMimeType.EqualsLiteral("audio/mp4a-latm"))) ||
     ((sIsVTAvailable || sIsVDAAvailable) &&
      (aMimeType.EqualsLiteral("video/mp4") ||
       aMimeType.EqualsLiteral("video/avc")));
 }

--- a/dom/media/platforms/apple/AppleDecoderModule.h
+++ b/dom/media/platforms/apple/AppleDecoderModule.h
@@ -27,17 +27,17 @@ public:
                      MediaDataDecoderCallback* aCallback) override;
 
   // Decode thread.
   already_AddRefed<MediaDataDecoder>
   CreateAudioDecoder(const AudioInfo& aConfig,
                      FlushableTaskQueue* aAudioTaskQueue,
                      MediaDataDecoderCallback* aCallback) override;
 
-  bool SupportsMimeType(const nsACString& aMimeType) override;
+  bool SupportsMimeType(const nsACString& aMimeType) const override;
 
   ConversionRequired
   DecoderNeedsConversion(const TrackInfo& aConfig) const override;
 
   static void Init();
 
   static bool sCanUseHardwareVideoDecoder;
 

--- a/dom/media/platforms/ffmpeg/FFmpegDecoderModule.h
+++ b/dom/media/platforms/ffmpeg/FFmpegDecoderModule.h
@@ -56,17 +56,17 @@ public:
                      FlushableTaskQueue* aAudioTaskQueue,
                      MediaDataDecoderCallback* aCallback) override
   {
     RefPtr<MediaDataDecoder> decoder =
       new FFmpegAudioDecoder<V>(aAudioTaskQueue, aCallback, aConfig);
     return decoder.forget();
   }
 
-  bool SupportsMimeType(const nsACString& aMimeType) override
+  bool SupportsMimeType(const nsACString& aMimeType) const override
   {
     AVCodecID audioCodec = FFmpegAudioDecoder<V>::GetCodecId(aMimeType);
     AVCodecID videoCodec = FFmpegH264Decoder<V>::GetCodecId(aMimeType);
     if (audioCodec == AV_CODEC_ID_NONE && videoCodec == AV_CODEC_ID_NONE) {
       return false;
     }
     AVCodecID codec = audioCodec != AV_CODEC_ID_NONE ? audioCodec : videoCodec;
     return !!FFmpegDataDecoder<V>::FindAVCodec(codec);

--- a/dom/media/platforms/gonk/GonkDecoderModule.cpp
+++ b/dom/media/platforms/gonk/GonkDecoderModule.cpp
@@ -56,17 +56,17 @@ GonkDecoderModule::DecoderNeedsConversio
   if (aConfig.IsVideo()) {
     return kNeedAnnexB;
   } else {
     return kNeedNone;
   }
 }
 
 bool
-GonkDecoderModule::SupportsMimeType(const nsACString& aMimeType)
+GonkDecoderModule::SupportsMimeType(const nsACString& aMimeType) const
 {
   return aMimeType.EqualsLiteral("audio/mp4a-latm") ||
     aMimeType.EqualsLiteral("audio/3gpp") ||
     aMimeType.EqualsLiteral("audio/amr-wb") ||
     aMimeType.EqualsLiteral("audio/mpeg") ||
     aMimeType.EqualsLiteral("video/mp4") ||
     aMimeType.EqualsLiteral("video/mp4v-es") ||
     aMimeType.EqualsLiteral("video/avc") ||

--- a/dom/media/platforms/gonk/GonkDecoderModule.h
+++ b/dom/media/platforms/gonk/GonkDecoderModule.h
@@ -30,15 +30,15 @@ public:
                      FlushableTaskQueue* aAudioTaskQueue,
                      MediaDataDecoderCallback* aCallback) override;
 
   static void Init();
 
   ConversionRequired
   DecoderNeedsConversion(const TrackInfo& aConfig) const override;
 
-  bool SupportsMimeType(const nsACString& aMimeType) override;
+  bool SupportsMimeType(const nsACString& aMimeType) const override;
 
 };
 
 } // namespace mozilla
 
 #endif

--- a/dom/media/platforms/wmf/WMFDecoderModule.cpp
+++ b/dom/media/platforms/wmf/WMFDecoderModule.cpp
@@ -159,17 +159,17 @@ CanCreateWMFDecoder()
   static Maybe<bool> result;
   if (result.isNothing()) {
     result.emplace(CanCreateMFTDecoder(aGuid));
   }
   return result.value();
 }
 
 bool
-WMFDecoderModule::SupportsMimeType(const nsACString& aMimeType)
+WMFDecoderModule::SupportsMimeType(const nsACString& aMimeType) const
 {
   if ((aMimeType.EqualsLiteral("audio/mp4a-latm") ||
        aMimeType.EqualsLiteral("audio/mp4")) &&
       CanCreateWMFDecoder<CLSID_CMSAACDecMFT>()) {
     return true;
   }
   if ((aMimeType.EqualsLiteral("video/avc") ||
        aMimeType.EqualsLiteral("video/mp4")) &&

--- a/dom/media/platforms/wmf/WMFDecoderModule.h
+++ b/dom/media/platforms/wmf/WMFDecoderModule.h
@@ -26,17 +26,17 @@ public:
                      FlushableTaskQueue* aVideoTaskQueue,
                      MediaDataDecoderCallback* aCallback) override;
 
   already_AddRefed<MediaDataDecoder>
   CreateAudioDecoder(const AudioInfo& aConfig,
                      FlushableTaskQueue* aAudioTaskQueue,
                      MediaDataDecoderCallback* aCallback) override;
 
-  bool SupportsMimeType(const nsACString& aMimeType) override;
+  bool SupportsMimeType(const nsACString& aMimeType) const override;
 
   ConversionRequired
   DecoderNeedsConversion(const TrackInfo& aConfig) const override;
 
   // Called on main thread.
   static void Init();
 
   // Called from any thread, must call init first