--- a/dom/base/Navigator.cpp
+++ b/dom/base/Navigator.cpp
@@ -2581,67 +2581,96 @@ Navigator::GetUserAgent(nsPIDOMWindowInn
 
   return siteSpecificUA->GetUserAgentForURIAndWindow(aURI, aWindow, aUserAgent);
 }
 
 #ifdef MOZ_EME
 static nsCString
 ToCString(const nsString& aString)
 {
-  return NS_ConvertUTF16toUTF8(aString);
+  nsCString str("'");
+  str.Append(NS_ConvertUTF16toUTF8(aString));
+  str.AppendLiteral("'");
+  return str;
+}
+
+static nsCString
+ToCString(const MediaKeysRequirement aValue)
+{
+  nsCString str("'");
+  str.Append(nsDependentCString(MediaKeysRequirementValues::strings[static_cast<uint32_t>(aValue)].value));
+  str.AppendLiteral("'");
+  return str;
 }
 
 static nsCString
 ToCString(const MediaKeySystemMediaCapability& aValue)
 {
   nsCString str;
-  str.AppendLiteral("{contentType='");
-  if (!aValue.mContentType.IsEmpty()) {
-    str.Append(ToCString(aValue.mContentType));
-  }
-  str.AppendLiteral("'}");
+  str.AppendLiteral("{contentType=");
+  str.Append(ToCString(aValue.mContentType));
+  str.AppendLiteral(", robustness=");
+  str.Append(ToCString(aValue.mRobustness));
+  str.AppendLiteral("}");
   return str;
 }
 
 template<class Type>
 static nsCString
 ToCString(const Sequence<Type>& aSequence)
 {
-  nsCString s;
-  s.AppendLiteral("[");
+  nsCString str;
+  str.AppendLiteral("[");
   for (size_t i = 0; i < aSequence.Length(); i++) {
     if (i != 0) {
-      s.AppendLiteral(",");
+      str.AppendLiteral(",");
     }
-    s.Append(ToCString(aSequence[i]));
+    str.Append(ToCString(aSequence[i]));
   }
-  s.AppendLiteral("]");
-  return s;
+  str.AppendLiteral("]");
+  return str;
+}
+
+template<class Type>
+static nsCString
+ToCString(const Optional<Sequence<Type>>& aOptional)
+{
+  nsCString str;
+  if (aOptional.WasPassed()) {
+    str.Append(ToCString(aOptional.Value()));
+  } else {
+    str.AppendLiteral("[]");
+  }
+  return str;
 }
 
 static nsCString
 ToCString(const MediaKeySystemConfiguration& aConfig)
 {
   nsCString str;
-  str.AppendLiteral("{");
-  str.AppendPrintf("label='%s'", NS_ConvertUTF16toUTF8(aConfig.mLabel).get());
-
-  if (aConfig.mInitDataTypes.WasPassed()) {
-    str.AppendLiteral(", initDataTypes=");
-    str.Append(ToCString(aConfig.mInitDataTypes.Value()));
-  }
-
-  if (aConfig.mAudioCapabilities.WasPassed()) {
-    str.AppendLiteral(", audioCapabilities=");
-    str.Append(ToCString(aConfig.mAudioCapabilities.Value()));
-  }
-  if (aConfig.mVideoCapabilities.WasPassed()) {
-    str.AppendLiteral(", videoCapabilities=");
-    str.Append(ToCString(aConfig.mVideoCapabilities.Value()));
-  }
+  str.AppendLiteral("{label=");
+  str.Append(ToCString(aConfig.mLabel));
+
+  str.AppendLiteral(", initDataTypes=");
+  str.Append(ToCString(aConfig.mInitDataTypes));
+
+  str.AppendLiteral(", audioCapabilities=");
+  str.Append(ToCString(aConfig.mAudioCapabilities));
+
+  str.AppendLiteral(", videoCapabilities=");
+  str.Append(ToCString(aConfig.mVideoCapabilities));
+
+  str.AppendLiteral(", distinctiveIdentifier=");
+  str.Append(ToCString(aConfig.mDistinctiveIdentifier));
+
+  str.AppendLiteral(", persistentState=");
+  str.Append(ToCString(aConfig.mPersistentState));
+
+  str.AppendLiteral(", sessionTypes=");
+  str.Append(ToCString(aConfig.mSessionTypes));
 
   str.AppendLiteral("}");
 
   return str;
 }
 
 static nsCString
 RequestKeySystemAccessLogString(const nsAString& aKeySystem,