diff --git a/media/mtransport/test/runnable_utils_unittest.cpp b/media/mtransport/test/runnable_utils_unittest.cpp
index 813f98f14dfa..cd2ba6c22883 100644
--- a/media/mtransport/test/runnable_utils_unittest.cpp
+++ b/media/mtransport/test/runnable_utils_unittest.cpp
@@ -44,7 +44,7 @@ class Destructor {
     *destroyed_ = true;
   }
  public:
-  Destructor(bool* destroyed) : destroyed_(destroyed) {}
+  explicit Destructor(bool* destroyed) : destroyed_(destroyed) {}
 
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(Destructor)
 
@@ -54,7 +54,7 @@ class Destructor {
 
 class TargetClass {
  public:
-  TargetClass(int *ran) : ran_(ran) {}
+  explicit TargetClass(int *ran) : ran_(ran) {}
 
   void m1(int x) {
     std::cerr << __FUNCTION__ << " " << x << std::endl;
diff --git a/media/mtransport/test/sockettransportservice_unittest.cpp b/media/mtransport/test/sockettransportservice_unittest.cpp
index e54b64dd67e7..2ad7cf56c967 100644
--- a/media/mtransport/test/sockettransportservice_unittest.cpp
+++ b/media/mtransport/test/sockettransportservice_unittest.cpp
@@ -78,7 +78,7 @@ class SocketTransportServiceTest : public ::testing::Test {
 // Received an event.
 class EventReceived : public nsRunnable {
 public:
-  EventReceived(SocketTransportServiceTest *test) :
+  explicit EventReceived(SocketTransportServiceTest *test) :
       test_(test) {}
 
   NS_IMETHOD Run() {
@@ -93,7 +93,7 @@ public:
 // Register our listener on the socket
 class RegisterEvent : public nsRunnable {
 public:
-  RegisterEvent(SocketTransportServiceTest *test) :
+  explicit RegisterEvent(SocketTransportServiceTest *test) :
       test_(test) {}
 
   NS_IMETHOD Run() {
@@ -107,7 +107,7 @@ public:
 
 class SocketHandler : public nsASocketHandler {
  public:
-  SocketHandler(SocketTransportServiceTest *test) : test_(test) {
+  explicit SocketHandler(SocketTransportServiceTest *test) : test_(test) {
   }
 
   void OnSocketReady(PRFileDesc *fd, int16_t outflags) {
diff --git a/media/mtransport/test/transport_unittests.cpp b/media/mtransport/test/transport_unittests.cpp
index 896c848e6dfa..27a7013ee3a9 100644
--- a/media/mtransport/test/transport_unittests.cpp
+++ b/media/mtransport/test/transport_unittests.cpp
@@ -334,7 +334,7 @@ class DtlsInspectorInjector : public DtlsRecordInspector {
 // Make a copy of the first instance of a message.
 class DtlsInspectorRecordHandshakeMessage : public DtlsRecordInspector {
  public:
-  DtlsInspectorRecordHandshakeMessage(uint8_t handshake_type)
+  explicit DtlsInspectorRecordHandshakeMessage(uint8_t handshake_type)
       : handshake_type_(handshake_type),
         buffer_() {}
 
diff --git a/media/webrtc/signaling/src/common/Wrapper.h b/media/webrtc/signaling/src/common/Wrapper.h
index 1d793dcb14c2..a88cbd4bf08c 100644
--- a/media/webrtc/signaling/src/common/Wrapper.h
+++ b/media/webrtc/signaling/src/common/Wrapper.h
@@ -69,7 +69,7 @@ private:
 
 class AutoLockNSPR {
 public:
-  AutoLockNSPR(LockNSPR& lock) : lock_(lock) {
+  explicit AutoLockNSPR(LockNSPR& lock) : lock_(lock) {
     lock_.Acquire();
   }
   ~AutoLockNSPR() {
diff --git a/media/webrtc/signaling/src/media-conduit/MediaConduitInterface.h b/media/webrtc/signaling/src/media-conduit/MediaConduitInterface.h
index 27b572b0e238..d8f141be98cb 100755
--- a/media/webrtc/signaling/src/media-conduit/MediaConduitInterface.h
+++ b/media/webrtc/signaling/src/media-conduit/MediaConduitInterface.h
@@ -54,7 +54,7 @@ public:
 class ImageHandle
 {
 public:
-  ImageHandle(layers::Image* image) : mImage(image) {}
+  explicit ImageHandle(layers::Image* image) : mImage(image) {}
 
   const RefPtr<layers::Image>& GetImage() const { return mImage; }
 
diff --git a/media/webrtc/signaling/src/media/CSFAudioControlWrapper.h b/media/webrtc/signaling/src/media/CSFAudioControlWrapper.h
index 5126da59d977..49f3b8923704 100644
--- a/media/webrtc/signaling/src/media/CSFAudioControlWrapper.h
+++ b/media/webrtc/signaling/src/media/CSFAudioControlWrapper.h
@@ -16,7 +16,7 @@ namespace CSF
 	public:
 		// device names are in UTF-8 encoding
 
-		AudioControlWrapper(AudioControl * audioControl){_realAudioControl = audioControl;};
+		explicit AudioControlWrapper(AudioControl * audioControl){_realAudioControl = audioControl;};
 		virtual std::vector<std::string> getRecordingDevices();
 		virtual std::vector<std::string> getPlayoutDevices();
 
diff --git a/media/webrtc/signaling/src/media/CSFVideoControlWrapper.h b/media/webrtc/signaling/src/media/CSFVideoControlWrapper.h
index 5f8ce585899c..226a7efaefc8 100644
--- a/media/webrtc/signaling/src/media/CSFVideoControlWrapper.h
+++ b/media/webrtc/signaling/src/media/CSFVideoControlWrapper.h
@@ -21,7 +21,7 @@ namespace CSF
 	class ECC_API VideoControlWrapper : public VideoControl
 	{
 	public:
-		VideoControlWrapper(VideoControl * videoControl){_realVideoControl = videoControl;};
+		explicit VideoControlWrapper(VideoControl * videoControl){_realVideoControl = videoControl;};
 
 		virtual void setVideoMode( bool enable );
 
diff --git a/media/webrtc/signaling/src/mediapipeline/MediaPipeline.h b/media/webrtc/signaling/src/mediapipeline/MediaPipeline.h
index c00471cc4d2f..00db9a013cc4 100644
--- a/media/webrtc/signaling/src/mediapipeline/MediaPipeline.h
+++ b/media/webrtc/signaling/src/mediapipeline/MediaPipeline.h
@@ -343,7 +343,7 @@ class GenericReceiveListener;
 class GenericReceiveCallback : public TrackAddedCallback
 {
  public:
-  GenericReceiveCallback(GenericReceiveListener* listener)
+  explicit GenericReceiveCallback(GenericReceiveListener* listener)
     : listener_(listener) {}
 
   void TrackAdded(TrackTicks time) {
@@ -357,7 +357,7 @@ class GenericReceiveCallback : public TrackAddedCallback
 class ConduitDeleteEvent: public nsRunnable
 {
 public:
-  ConduitDeleteEvent(TemporaryRef<MediaSessionConduit> aConduit) :
+  explicit ConduitDeleteEvent(TemporaryRef<MediaSessionConduit> aConduit) :
     mConduit(aConduit) {}
 
   /* we exist solely to proxy release of the conduit */
@@ -435,7 +435,7 @@ public:
   class PipelineListener : public MediaStreamDirectListener {
    friend class MediaPipelineTransmit;
    public:
-    PipelineListener(const RefPtr<MediaSessionConduit>& conduit)
+    explicit PipelineListener(const RefPtr<MediaSessionConduit>& conduit)
       : conduit_(conduit),
         track_id_(TRACK_INVALID),
         mMutex("MediaPipelineTransmit::PipelineListener"),
@@ -692,7 +692,7 @@ class MediaPipelineReceiveVideo : public MediaPipelineReceive {
  private:
   class PipelineRenderer : public VideoRenderer {
    public:
-    PipelineRenderer(MediaPipelineReceiveVideo *pipeline) :
+    explicit PipelineRenderer(MediaPipelineReceiveVideo *pipeline) :
       pipeline_(pipeline) {}
 
     void Detach() { pipeline_ = nullptr; }
diff --git a/media/webrtc/signaling/src/peerconnection/PeerConnectionCtx.h b/media/webrtc/signaling/src/peerconnection/PeerConnectionCtx.h
index 3aaa39033443..d6af2b54243c 100644
--- a/media/webrtc/signaling/src/peerconnection/PeerConnectionCtx.h
+++ b/media/webrtc/signaling/src/peerconnection/PeerConnectionCtx.h
@@ -35,7 +35,7 @@ class WebrtcGlobalInformation;
 class SipccOfferOptions {
 public:
   SipccOfferOptions();
-  SipccOfferOptions(const dom::RTCOfferOptions &aOther);
+  explicit SipccOfferOptions(const dom::RTCOfferOptions &aOther);
   cc_media_options_t* build() const;
 protected:
   cc_media_options_t mOptions;
diff --git a/media/webrtc/signaling/src/peerconnection/PeerConnectionMedia.h b/media/webrtc/signaling/src/peerconnection/PeerConnectionMedia.h
index c4ecc79baa64..7a2f3f34a2bd 100644
--- a/media/webrtc/signaling/src/peerconnection/PeerConnectionMedia.h
+++ b/media/webrtc/signaling/src/peerconnection/PeerConnectionMedia.h
@@ -57,7 +57,7 @@ class Fake_AudioGenerator {
  public:
   typedef mozilla::DOMMediaStream DOMMediaStream;
 
-Fake_AudioGenerator(DOMMediaStream* aStream) : mStream(aStream), mCount(0) {
+  explicit Fake_AudioGenerator(DOMMediaStream* aStream) : mStream(aStream), mCount(0) {
     mTimer = do_CreateInstance("@mozilla.org/timer;1");
     MOZ_ASSERT(mTimer);
 
@@ -99,7 +99,7 @@ class Fake_VideoGenerator {
   typedef mozilla::DOMMediaStream DOMMediaStream;
   typedef mozilla::gfx::IntSize IntSize;
 
-  Fake_VideoGenerator(DOMMediaStream* aStream) {
+  explicit Fake_VideoGenerator(DOMMediaStream* aStream) {
     mStream = aStream;
     mCount = 0;
     mTimer = do_CreateInstance("@mozilla.org/timer;1");
@@ -289,7 +289,7 @@ class PeerConnectionMedia : public sigslot::has_slots<> {
   ~PeerConnectionMedia() {}
 
  public:
-  PeerConnectionMedia(PeerConnectionImpl *parent);
+  explicit PeerConnectionMedia(PeerConnectionImpl *parent);
 
   nsresult Init(const std::vector<mozilla::NrIceStunServer>& stun_servers,
                 const std::vector<mozilla::NrIceTurnServer>& turn_servers);
diff --git a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCall.h b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCall.h
index 6b6352c8dbce..8164f8179299 100644
--- a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCall.h
+++ b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCall.h
@@ -64,7 +64,7 @@ namespace CSF
     CSF_DECLARE_WRAP(CC_SIPCCCall, cc_call_handle_t);
     private:
         cc_call_handle_t callHandle;
-        CC_SIPCCCall (cc_call_handle_t aCallHandle);
+        explicit CC_SIPCCCall (cc_call_handle_t aCallHandle);
         CC_SIPCCCallMediaDataPtr  pMediaData;
         std::string peerconnection;  // The peerconnection handle
 
diff --git a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCallInfo.h b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCallInfo.h
index 127b2e6f68d9..fb6dd057c03e 100644
--- a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCallInfo.h
+++ b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCallInfo.h
@@ -25,7 +25,7 @@ namespace CSF
     private:
     	cc_callinfo_ref_t callinfo_ref;
 
-        CC_SIPCCCallInfo (cc_callinfo_ref_t callinfo);
+        explicit CC_SIPCCCallInfo (cc_callinfo_ref_t callinfo);
 
         CSF_DECLARE_WRAP(CC_SIPCCCallInfo, cc_callinfo_ref_t);
 
diff --git a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCallServerInfo.h b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCallServerInfo.h
index 3a7062c01820..2d425d7666fe 100644
--- a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCallServerInfo.h
+++ b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCCallServerInfo.h
@@ -17,7 +17,7 @@ namespace CSF
     private:
         cc_callserver_ref_t callserverinfo_ref;
 
-        CC_SIPCCCallServerInfo (cc_callserver_ref_t aCallServerInfo);
+        explicit CC_SIPCCCallServerInfo (cc_callserver_ref_t aCallServerInfo);
 
         CSF_DECLARE_WRAP(CC_SIPCCCallServerInfo, cc_callserver_ref_t);
 
diff --git a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCDevice.h b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCDevice.h
index a7da9ffacfd1..fb5f9867dbb8 100644
--- a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCDevice.h
+++ b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCDevice.h
@@ -18,7 +18,7 @@ namespace CSF
     	CSF_DECLARE_WRAP(CC_SIPCCDevice, cc_device_handle_t);
         static CC_DevicePtr create (const std::string & phoneConfigFileNameStr);
 
-        CC_SIPCCDevice (cc_device_handle_t aDeviceHandle);
+        explicit CC_SIPCCDevice (cc_device_handle_t aDeviceHandle);
 
     public:
 
diff --git a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCDeviceInfo.h b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCDeviceInfo.h
index d89ce895a7fd..2119a3317bea 100644
--- a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCDeviceInfo.h
+++ b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCDeviceInfo.h
@@ -15,7 +15,7 @@ namespace CSF
     class CC_SIPCCDeviceInfo : public CC_DeviceInfo
     {
     private:
-        CC_SIPCCDeviceInfo (cc_deviceinfo_ref_t aDeviceInfo);
+        explicit CC_SIPCCDeviceInfo (cc_deviceinfo_ref_t aDeviceInfo);
         cc_deviceinfo_ref_t deviceinfo_ref;
 
         CSF_DECLARE_WRAP(CC_SIPCCDeviceInfo, cc_deviceinfo_ref_t);
diff --git a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCFeatureInfo.h b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCFeatureInfo.h
index a719d8d3ff12..83d6817c0dd6 100644
--- a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCFeatureInfo.h
+++ b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCFeatureInfo.h
@@ -16,7 +16,7 @@ namespace CSF
     {
     private:
         cc_featureinfo_ref_t featureinfo_ref;
-        CC_SIPCCFeatureInfo (cc_featureinfo_ref_t aFeatureInfo);
+        explicit CC_SIPCCFeatureInfo (cc_featureinfo_ref_t aFeatureInfo);
         CSF_DECLARE_WRAP(CC_SIPCCFeatureInfo, cc_featureinfo_ref_t);
 
     public:
diff --git a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCLine.h b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCLine.h
index d7c9c10d20a4..68d627b0b479 100644
--- a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCLine.h
+++ b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCLine.h
@@ -20,7 +20,7 @@ namespace CSF
         CSF_DECLARE_WRAP(CC_SIPCCLine, cc_lineid_t);
 
         cc_lineid_t lineId;
-        CC_SIPCCLine (cc_lineid_t aLineId) : lineId(aLineId) { }
+        explicit CC_SIPCCLine (cc_lineid_t aLineId) : lineId(aLineId) { }
 
     public:
         virtual std::string toString() {
diff --git a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCLineInfo.h b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCLineInfo.h
index fb525a74af79..e6126fef6973 100644
--- a/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCLineInfo.h
+++ b/media/webrtc/signaling/src/softphonewrapper/CC_SIPCCLineInfo.h
@@ -19,7 +19,7 @@ namespace CSF
 
     private:
         cc_lineinfo_ref_t lineinfo;
-        CC_SIPCCLineInfo (cc_lineinfo_ref_t lineinfo);
+        explicit CC_SIPCCLineInfo (cc_lineinfo_ref_t lineinfo);
         CSF_DECLARE_WRAP(CC_SIPCCLineInfo, cc_lineinfo_ref_t);
 
     public:
diff --git a/media/webrtc/signaling/test/FakeMediaStreams.h b/media/webrtc/signaling/test/FakeMediaStreams.h
index 16733c4372b2..0ce658f4a9ab 100644
--- a/media/webrtc/signaling/test/FakeMediaStreams.h
+++ b/media/webrtc/signaling/test/FakeMediaStreams.h
@@ -104,8 +104,8 @@ class Fake_MediaStream {
 
 class Fake_MediaPeriodic : public nsITimerCallback {
 public:
-Fake_MediaPeriodic(Fake_MediaStream *aStream) : mStream(aStream),
-                                                mCount(0) {}
+  explicit Fake_MediaPeriodic(Fake_MediaStream *aStream) : mStream(aStream),
+                                                           mCount(0) {}
   void Detach() {
     mStream = nullptr;
   }
@@ -217,7 +217,7 @@ class Fake_DOMMediaStream;
 class Fake_MediaStreamTrack : public mozilla::RefCounted<Fake_MediaStreamTrack>
 {
 public:
-  Fake_MediaStreamTrack(bool aIsVideo) : mIsVideo (aIsVideo) {}
+  explicit Fake_MediaStreamTrack(bool aIsVideo) : mIsVideo (aIsVideo) {}
   mozilla::TrackID GetTrackID() { return mIsVideo ? 1 : 0; }
   Fake_DOMMediaStream *GetStream() { return nullptr; }
   const Fake_MediaStreamTrack* AsVideoStreamTrack() const
@@ -241,7 +241,7 @@ protected:
   }
 
 public:
-  Fake_DOMMediaStream(Fake_MediaStream *stream = nullptr)
+  explicit Fake_DOMMediaStream(Fake_MediaStream *stream = nullptr)
     : mMediaStream(stream? stream : new Fake_MediaStream())
     , mVideoTrack(new Fake_MediaStreamTrack(true))
     , mAudioTrack(new Fake_MediaStreamTrack(false)) {}
diff --git a/media/webrtc/signaling/test/signaling_unittests.cpp b/media/webrtc/signaling/test/signaling_unittests.cpp
index b1dbe0880603..71bf59afbdf5 100644
--- a/media/webrtc/signaling/test/signaling_unittests.cpp
+++ b/media/webrtc/signaling/test/signaling_unittests.cpp
@@ -527,7 +527,7 @@ TestObserver::OnAddIceCandidateError(uint32_t code, const char *message, ER&)
 class ParsedSDP {
  public:
 
-  ParsedSDP(const std::string &sdp)
+  explicit ParsedSDP(const std::string &sdp)
   {
     Parse(sdp);
   }
@@ -684,7 +684,7 @@ class PCDispatchWrapper : public nsSupportsWeakReference
   virtual ~PCDispatchWrapper() {}
 
  public:
-  PCDispatchWrapper(sipcc::PeerConnectionImpl *peerConnection) {
+  explicit PCDispatchWrapper(sipcc::PeerConnectionImpl *peerConnection) {
     pc_ = peerConnection;
   }
 
@@ -941,7 +941,7 @@ NS_IMPL_ISUPPORTS(PCDispatchWrapper, nsISupportsWeakReference)
 
 class SignalingAgent {
  public:
-  SignalingAgent(const std::string &aName,
+  explicit SignalingAgent(const std::string &aName,
     const std::string stun_addr = g_stun_server_address,
     uint16_t stun_port = g_stun_server_port) : pc(nullptr), name(aName) {
     cfg_.addStunServer(stun_addr, stun_port);
@@ -1972,7 +1972,7 @@ static void SetMaxFsFr(nsCOMPtr<nsIPrefBranch> prefs,
 
 class FsFrPrefClearer {
   public:
-    FsFrPrefClearer(nsCOMPtr<nsIPrefBranch> prefs): mPrefs(prefs) {}
+    explicit FsFrPrefClearer(nsCOMPtr<nsIPrefBranch> prefs): mPrefs(prefs) {}
     ~FsFrPrefClearer() {
       gMainThread->Dispatch(
         WrapRunnableNM(FsFrPrefClearer::ClearUserPrefOnMainThread,