--- a/dom/media/MediaManager.cpp
+++ b/dom/media/MediaManager.cpp
@@ -1920,18 +1920,17 @@ MediaManager::GetUserMedia(nsPIDOMWindow
       case dom::MediaSourceEnum::Browser:
         // If no window id is passed in then default to the caller's window.
         // Functional defaults are helpful in tests, but also a natural outcome
         // of the constraints API's limited semantics for requiring input.
         if (!vc.mBrowserWindow.WasPassed()) {
           nsPIDOMWindow *outer = aWindow->GetOuterWindow();
           vc.mBrowserWindow.Construct(outer->WindowID());
         }
-        // | Fall through
-        // V
+        MOZ_FALLTHROUGH;
       case dom::MediaSourceEnum::Screen:
       case dom::MediaSourceEnum::Application:
       case dom::MediaSourceEnum::Window:
         // Deny screensharing request if support is disabled, or
         // the requesting document is not from a host on the whitelist, or
         // we're on Mac OSX 10.6 and WinXP until proved that they work
         if (!Preferences::GetBool(((videoType == dom::MediaSourceEnum::Browser)?
                                    "media.getusermedia.browser.enabled" :

--- a/dom/media/VideoUtils.cpp
+++ b/dom/media/VideoUtils.cpp
@@ -247,17 +247,17 @@ IsValidVideoRegion(const nsIntSize& aFra
 already_AddRefed<SharedThreadPool> GetMediaThreadPool(MediaThreadType aType)
 {
   const char *name;
   switch (aType) {
     case MediaThreadType::PLATFORM_DECODER:
       name = "MediaPDecoder";
       break;
     default:
-      MOZ_ASSERT(false);
+      MOZ_FALLTHROUGH_ASSERT("Unexpected MediaThreadType");
     case MediaThreadType::PLAYBACK:
       name = "MediaPlayback";
       break;
   }
   return SharedThreadPool::
     Get(nsDependentCString(name),
         Preferences::GetUint("media.num-decode-threads", 12));
 }

--- a/dom/media/webaudio/AudioEventTimeline.h
+++ b/dom/media/webaudio/AudioEventTimeline.h
@@ -564,17 +564,17 @@ public:
         case AudioTimelineEvent::ExponentialRamp:
           // The value will be constant after the last event
           return aPrevious->mValue;
         case AudioTimelineEvent::SetValueCurve:
           return ExtractValueFromCurve(aPrevious->template Time<TimeType>(),
                                        aPrevious->mCurve, aPrevious->mCurveLength,
                                        aPrevious->mDuration, aTime);
         case AudioTimelineEvent::SetTarget:
-          MOZ_ASSERT(false, "unreached");
+          MOZ_FALLTHROUGH_ASSERT("AudioTimelineEvent::SetTarget");
         case AudioTimelineEvent::SetValue:
         case AudioTimelineEvent::Cancel:
         case AudioTimelineEvent::Stream:
           MOZ_ASSERT(false, "Should have been handled earlier.");
       }
       MOZ_ASSERT(false, "unreached");
     }
 
@@ -612,17 +612,17 @@ public:
       // If the next event type is neither linear or exponential ramp, the
       // value is constant.
       return aPrevious->mValue;
     case AudioTimelineEvent::SetValueCurve:
       return ExtractValueFromCurve(aPrevious->template Time<TimeType>(),
                                    aPrevious->mCurve, aPrevious->mCurveLength,
                                    aPrevious->mDuration, aTime);
     case AudioTimelineEvent::SetTarget:
-      MOZ_ASSERT(false, "unreached");
+      MOZ_FALLTHROUGH_ASSERT("AudioTimelineEvent::SetTarget");
     case AudioTimelineEvent::SetValue:
     case AudioTimelineEvent::Cancel:
     case AudioTimelineEvent::Stream:
       MOZ_ASSERT(false, "Should have been handled earlier.");
     }
 
     MOZ_ASSERT(false, "unreached");
     return 0.0f;

--- a/dom/media/webaudio/MediaBufferDecoder.cpp
+++ b/dom/media/webaudio/MediaBufferDecoder.cpp
@@ -565,17 +565,17 @@ WebAudioDecodeJob::OnSuccess(ErrorCode a
 void
 WebAudioDecodeJob::OnFailure(ErrorCode aErrorCode)
 {
   MOZ_ASSERT(NS_IsMainThread());
 
   const char* errorMessage;
   switch (aErrorCode) {
   case NoError:
-    MOZ_ASSERT(false, "Who passed NoError to OnFailure?");
+    MOZ_FALLTHROUGH_ASSERT("Who passed NoError to OnFailure?");
     // Fall through to get some sort of a sane error message if this actually
     // happens at runtime.
   case UnknownError:
     errorMessage = "MediaDecodeAudioDataUnknownError";
     break;
   case UnknownContent:
     errorMessage = "MediaDecodeAudioDataUnknownContentType";
     break;

--- a/dom/media/webm/WebMBufferedParser.cpp
+++ b/dom/media/webm/WebMBufferedParser.cpp
@@ -128,17 +128,17 @@ void WebMBufferedParser::Append(const un
         break;
       case TRACKS_ID:
         mSkipBytes = mElement.mSize.mValue;
         mState = CHECK_INIT_FOUND;
         break;
       case EBML_ID:
         mLastInitStartOffset = mCurrentOffset + (p - aBuffer) -
                             (mElement.mID.mLength + mElement.mSize.mLength);
-        /* FALLTHROUGH */
+        MOZ_FALLTHROUGH;
       default:
         mSkipBytes = mElement.mSize.mValue;
         mState = SKIP_DATA;
         mNextState = READ_ELEMENT_ID;
         break;
       }
       break;
     case READ_VINT: {