--- a/dom/locales/en-US/chrome/dom/dom.properties
+++ b/dom/locales/en-US/chrome/dom/dom.properties
@@ -119,17 +119,17 @@ MediaLoadInvalidURI=Invalid URI. Load of
 # LOCALIZATION NOTE: %1$S is the media resource's format/codec type (basically equivalent to the file type, e.g. MP4,AVI,WMV,MOV etc), %2$S is the URL of the media resource which failed to load.
 MediaLoadUnsupportedTypeAttribute=Specified “type” attribute of “%1$S” is not supported. Load of media resource %2$S failed.
 # LOCALIZATION NOTE: %1$S is the "media" attribute value of the <source> element. It is a media query. %2$S is the URL of the media resource which failed to load.
 MediaLoadSourceMediaNotMatched=Specified “media” attribute of “%1$S” does not match the environment. Load of media resource %2$S failed.
 # LOCALIZATION NOTE: %1$S is the MIME type HTTP header being sent by the web server, %2$S is the URL of the media resource which failed to load.
 MediaLoadUnsupportedMimeType=HTTP “Content-Type” of “%1$S” is not supported. Load of media resource %2$S failed.
 # LOCALIZATION NOTE: %S is the URL of the media resource which failed to load because of error in decoding.
 MediaLoadDecodeError=Media resource %S could not be decoded.
-MediaWidevineNoWMFNoSilverlight=Trying to play Widevine with no Windows Media Foundation (nor Silverlight fallback), see https://support.mozilla.org/kb/fix-video-audio-problems-firefox-windows
+MediaWidevineNoWMF=Trying to play Widevine with no Windows Media Foundation. See https://support.mozilla.org/kb/fix-video-audio-problems-firefox-windows
 # LOCALIZATION NOTE: %S is a comma-separated list of codecs (e.g. 'video/mp4, video/webm')
 MediaWMFNeeded=To play video formats %S, you need to install extra Microsoft software, see https://support.mozilla.org/kb/fix-video-audio-problems-firefox-windows
 # LOCALIZATION NOTE: %S is a comma-separated list of codecs (e.g. 'video/mp4, video/webm')
 MediaUnsupportedBeforeWindowsVista=Video formats %S unsupported by Microsoft before Windows Vista
 # LOCALIZATION NOTE: %S is a comma-separated list of codecs (e.g. 'video/mp4, video/webm')
 MediaPlatformDecoderNotFound=The video on this page can’t be played. Your system may not have the required video codecs for: %S
 MediaUnsupportedLibavcodec=The video on this page can’t be played. Your system has an unsupported version of libavcodec
 # LOCALIZATION NOTE: %S is a comma-separated list of codecs (e.g. 'video/mp4, video/webm')

--- a/dom/media/DecoderDoctorDiagnostics.cpp
+++ b/dom/media/DecoderDoctorDiagnostics.cpp
@@ -245,19 +245,19 @@ DecoderDoctorDocumentWatcher::EnsureTime
     if (NS_WARN_IF(NS_FAILED(
           mTimer->InitWithCallback(
             this, sAnalysisPeriod_ms, nsITimer::TYPE_ONE_SHOT)))) {
       mTimer = nullptr;
     }
   }
 }
 
-static const NotificationAndReportStringId sMediaWidevineNoWMFNoSilverlight =
+static const NotificationAndReportStringId sMediaWidevineNoWMF=
   { dom::DecoderDoctorNotificationType::Platform_decoder_not_found,
-    "MediaWidevineNoWMFNoSilverlight" };
+    "MediaWidevineNoWMF" };
 static const NotificationAndReportStringId sMediaWMFNeeded =
   { dom::DecoderDoctorNotificationType::Platform_decoder_not_found,
     "MediaWMFNeeded" };
 static const NotificationAndReportStringId sMediaUnsupportedBeforeWindowsVista =
   { dom::DecoderDoctorNotificationType::Platform_decoder_not_found,
     "MediaUnsupportedBeforeWindowsVista" };
 static const NotificationAndReportStringId sMediaPlatformDecoderNotFound =
   { dom::DecoderDoctorNotificationType::Platform_decoder_not_found,
@@ -270,20 +270,20 @@ static const NotificationAndReportString
     "MediaNoDecoders" };
 static const NotificationAndReportStringId sCannotInitializePulseAudio =
   { dom::DecoderDoctorNotificationType::Cannot_initialize_pulseaudio,
     "MediaCannotInitializePulseAudio" };
 static const NotificationAndReportStringId sUnsupportedLibavcodec =
   { dom::DecoderDoctorNotificationType::Unsupported_libavcodec,
     "MediaUnsupportedLibavcodec" };
 
-static const NotificationAndReportStringId*
+static const NotificationAndReportStringId *const
 sAllNotificationsAndReportStringIds[] =
 {
-  &sMediaWidevineNoWMFNoSilverlight,
+  &sMediaWidevineNoWMF,
   &sMediaWMFNeeded,
   &sMediaUnsupportedBeforeWindowsVista,
   &sMediaPlatformDecoderNotFound,
   &sMediaCannotPlayNoDecoders,
   &sMediaNoDecoders,
   &sCannotInitializePulseAudio,
   &sUnsupportedLibavcodec,
 };
@@ -370,43 +370,16 @@ ReportAnalysis(nsIDocument* aDocument,
   filter.StripWhitespace();
   if (filter.EqualsLiteral("*")
       || StringListContains(filter, aNotification.mReportStringId)) {
     DispatchNotification(
       aDocument->GetInnerWindow(), aNotification, aIsSolved, aParams);
   }
 }
 
-enum SilverlightPresence {
-  eNoSilverlight,
-  eSilverlightDisabled,
-  eSilverlightEnabled
-};
-static SilverlightPresence
-CheckSilverlight()
-{
-  MOZ_ASSERT(NS_IsMainThread());
-  RefPtr<nsPluginHost> pluginHost = nsPluginHost::GetInst();
-  if (!pluginHost) {
-    return eNoSilverlight;
-  }
-  nsTArray<nsCOMPtr<nsIInternalPluginTag>> plugins;
-  pluginHost->GetPlugins(plugins, /*aIncludeDisabled*/ true);
-  for (const auto& plugin : plugins) {
-    for (const auto& mime : plugin->MimeTypes()) {
-      if (mime.LowerCaseEqualsLiteral("application/x-silverlight")
-          || mime.LowerCaseEqualsLiteral("application/x-silverlight-2")) {
-        return plugin->IsEnabled() ? eSilverlightEnabled : eSilverlightDisabled;
-      }
-    }
-  }
-
-  return eNoSilverlight;
-}
-
 static nsString
 CleanItemForFormatsList(const nsAString& aItem)
 {
   nsString item(aItem);
   // Remove commas from item, as commas are used to separate items. It's fine
   // to have a one-way mapping, it's only used for comparisons and in
   // console display (where formats shouldn't contain commas in the first place)
   item.ReplaceChar(',', ' ');
@@ -549,24 +522,21 @@ DecoderDoctorDocumentWatcher::Synthesize
     }
   }
 
   // Look at Key System issues first, as they take precedence over format checks.
   if (!unsupportedKeySystems.IsEmpty() && supportedKeySystems.IsEmpty()) {
     // No supported key systems!
     switch (lastKeySystemIssue) {
       case DecoderDoctorDiagnostics::eWidevineWithNoWMF:
-        if (CheckSilverlight() != eSilverlightEnabled) {
-          DD_INFO("DecoderDoctorDocumentWatcher[%p, doc=%p]::SynthesizeAnalysis() - unsupported key systems: %s, widevine without WMF nor Silverlight",
-                  this, mDocument, NS_ConvertUTF16toUTF8(unsupportedKeySystems).get());
-          ReportAnalysis(mDocument, sMediaWidevineNoWMFNoSilverlight,
-                         false, unsupportedKeySystems);
-          return;
-        }
-        break;
+        DD_INFO("DecoderDoctorDocumentWatcher[%p, doc=%p]::SynthesizeAnalysis() - unsupported key systems: %s, Widevine without WMF",
+                this, mDocument, NS_ConvertUTF16toUTF8(unsupportedKeySystems).get());
+        ReportAnalysis(mDocument, sMediaWidevineNoWMF, false,
+                       unsupportedKeySystems);
+        return;
       default:
         break;
     }
   }
 
   // Next, check playability of requested formats.
   if (!unplayableFormats.IsEmpty()) {
     // Some requested formats cannot be played.

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -396,17 +396,17 @@ pref("media.apple.mp4.enabled", true);
 // media.gmp.storage.version.observed, and if the versions don't match,
 // we clear storage and set media.gmp.storage.version.observed=expected.
 // This provides a mechanism to clear GMP storage when non-compatible
 // changes are made.
 pref("media.gmp.storage.version.expected", 1);
 
 // Filter what triggers user notifications.
 // See DecoderDoctorDocumentWatcher::ReportAnalysis for details.
-pref("media.decoder-doctor.notifications-allowed", "MediaWMFNeeded,MediaWidevineNoWMFNoSilverlight,MediaCannotInitializePulseAudio,MediaCannotPlayNoDecoders,MediaUnsupportedLibavcodec");
+pref("media.decoder-doctor.notifications-allowed", "MediaWMFNeeded,MediaWidevineNoWMF,MediaCannotInitializePulseAudio,MediaCannotPlayNoDecoders,MediaUnsupportedLibavcodec");
 // Whether we report partial failures.
 pref("media.decoder-doctor.verbose", false);
 // Whether DD should consider WMF-disabled a WMF failure, useful for testing.
 pref("media.decoder-doctor.wmf-disabled-is-failure", false);
 
 // Whether to suspend decoding of videos in background tabs.
 #ifdef NIGHTLY_BUILD
 pref("media.suspend-bkgnd-video.enabled", true);