diff --git a/dom/media/mediasource/MediaSourceDecoder.cpp b/dom/media/mediasource/MediaSourceDecoder.cpp
index 09f8520a731..db788873dd2 100644
--- a/dom/media/mediasource/MediaSourceDecoder.cpp
+++ b/dom/media/mediasource/MediaSourceDecoder.cpp
@@ -290,6 +290,12 @@ MediaSourceDecoder::PrepareReaderInitialization()
   mReader->PrepareInitialization();
 }
 
+void
+MediaSourceDecoder::GetMozDebugReaderData(nsAString& aString)
+{
+  mReader->GetMozDebugReaderData(aString);
+}
+
 #ifdef MOZ_EME
 nsresult
 MediaSourceDecoder::SetCDMProxy(CDMProxy* aProxy)
diff --git a/dom/media/mediasource/MediaSourceDecoder.h b/dom/media/mediasource/MediaSourceDecoder.h
index 6ac68a54c67..2800e7de7ed 100644
--- a/dom/media/mediasource/MediaSourceDecoder.h
+++ b/dom/media/mediasource/MediaSourceDecoder.h
@@ -79,6 +79,10 @@ public:
   // reader in this decoders MediaSourceReader.
   bool IsActiveReader(MediaDecoderReader* aReader);
 
+  // Returns a string describing the state of the MediaSource internal
+  // buffered data. Used for debugging purposes.
+  void GetMozDebugReaderData(nsAString& aString);
+
 private:
   void DoSetMediaSourceDuration(double aDuration);
   void ScheduleDurationChange(double aOldDuration,
diff --git a/dom/media/mediasource/MediaSourceReader.cpp b/dom/media/mediasource/MediaSourceReader.cpp
index 9b6cff6e8fe..a31dc384a85 100644
--- a/dom/media/mediasource/MediaSourceReader.cpp
+++ b/dom/media/mediasource/MediaSourceReader.cpp
@@ -13,6 +13,7 @@
 #include "MediaSourceUtils.h"
 #include "SourceBufferDecoder.h"
 #include "TrackBuffer.h"
+#include "nsPrintfCString.h"
 
 #ifdef MOZ_FMP4
 #include "SharedDecoderManager.h"
@@ -968,6 +969,40 @@ MediaSourceReader::SetMediaSourceDuration(double aDuration)
   mMediaSourceDuration = aDuration;
 }
 
+void
+MediaSourceReader::GetMozDebugReaderData(nsAString& aString)
+{
+  ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
+  nsAutoCString result;
+  result += nsPrintfCString("Dumping data for reader %p:\n", this);
+  if (mAudioTrack) {
+    result += nsPrintfCString("\tDumping Audio Track Decoders: - mLastAudioTime: %f\n", double(mLastAudioTime) / USECS_PER_S);
+    for (int32_t i = mAudioTrack->Decoders().Length() - 1; i >= 0; --i) {
+      nsRefPtr<MediaDecoderReader> newReader = mAudioTrack->Decoders()[i]->GetReader();
+
+      nsRefPtr<dom::TimeRanges> ranges = new dom::TimeRanges();
+      mAudioTrack->Decoders()[i]->GetBuffered(ranges);
+      result += nsPrintfCString("\t\tReader %d: %p ranges=%s active=%s\n",
+                                i, newReader.get(), DumpTimeRanges(ranges).get(),
+                                newReader.get() == mAudioReader.get() ? "true" : "false");
+    }
+  }
+
+  if (mVideoTrack) {
+    result += nsPrintfCString("\tDumping Video Track Decoders - mLastVideoTime: %f\n", double(mLastVideoTime) / USECS_PER_S);
+    for (int32_t i = mVideoTrack->Decoders().Length() - 1; i >= 0; --i) {
+      nsRefPtr<MediaDecoderReader> newReader = mVideoTrack->Decoders()[i]->GetReader();
+
+      nsRefPtr<dom::TimeRanges> ranges = new dom::TimeRanges();
+      mVideoTrack->Decoders()[i]->GetBuffered(ranges);
+      result += nsPrintfCString("\t\tReader %d: %p ranges=%s active=%s\n",
+                                i, newReader.get(), DumpTimeRanges(ranges).get(),
+                                newReader.get() == mVideoReader.get() ? "true" : "false");
+    }
+  }
+  aString += NS_ConvertUTF8toUTF16(result);
+}
+
 #ifdef MOZ_EME
 nsresult
 MediaSourceReader::SetCDMProxy(CDMProxy* aProxy)
diff --git a/dom/media/mediasource/MediaSourceReader.h b/dom/media/mediasource/MediaSourceReader.h
index 8d547af9194..c699554be38 100644
--- a/dom/media/mediasource/MediaSourceReader.h
+++ b/dom/media/mediasource/MediaSourceReader.h
@@ -146,6 +146,10 @@ public:
   // Returns true if aReader is a currently active audio or video
   bool IsActiveReader(MediaDecoderReader* aReader);
 
+  // Returns a string describing the state of the MediaSource internal
+  // buffered data. Used for debugging purposes.
+  void GetMozDebugReaderData(nsAString& aString);
+
 private:
   // Switch the current audio/video reader to the reader that
   // contains aTarget (or up to aError after target). Both