diff --git a/docshell/shistory/src/nsSHEntryShared.cpp b/docshell/shistory/src/nsSHEntryShared.cpp
index 1b27be5ea63..b2c173030b5 100644
--- a/docshell/shistory/src/nsSHEntryShared.cpp
+++ b/docshell/shistory/src/nsSHEntryShared.cpp
@@ -34,7 +34,7 @@ uint64_t gSHEntrySharedID = 0;
 typedef nsExpirationTracker<nsSHEntryShared, 3> HistoryTrackerBase;
 class HistoryTracker MOZ_FINAL : public HistoryTrackerBase {
 public:
-  HistoryTracker(uint32_t aTimeout)
+  explicit HistoryTracker(uint32_t aTimeout)
     : HistoryTrackerBase(1000 * aTimeout / 2)
   {
   }
diff --git a/dom/canvas/CanvasRenderingContext2D.cpp b/dom/canvas/CanvasRenderingContext2D.cpp
index 4165fac8986..cadaad5274b 100644
--- a/dom/canvas/CanvasRenderingContext2D.cpp
+++ b/dom/canvas/CanvasRenderingContext2D.cpp
@@ -695,7 +695,7 @@ NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(CanvasPattern, mContext)
 class CanvasDrawObserver
 {
 public:
-  CanvasDrawObserver(CanvasRenderingContext2D* aCanvasContext);
+  explicit CanvasDrawObserver(CanvasRenderingContext2D* aCanvasContext);
 
   // Only enumerate draw calls that could affect the heuristic
   enum DrawCallType {
diff --git a/dom/canvas/WebGLBindableName.h b/dom/canvas/WebGLBindableName.h
index 4a7f6c20831..d92616fb292 100644
--- a/dom/canvas/WebGLBindableName.h
+++ b/dom/canvas/WebGLBindableName.h
@@ -54,9 +54,9 @@ class WebGLBindableName
 {
 public:
 
-    WebGLBindableName(GLuint name)
+    explicit WebGLBindableName(GLuint aName)
         : WebGLBindable<T>()
-        , mGLName(name)
+        , mGLName(aName)
     { }
     GLuint GLName() const { return mGLName; }
 
diff --git a/dom/geolocation/nsGeolocationSettings.h b/dom/geolocation/nsGeolocationSettings.h
index f9986d921e5..f7c69201591 100644
--- a/dom/geolocation/nsGeolocationSettings.h
+++ b/dom/geolocation/nsGeolocationSettings.h
@@ -57,7 +57,7 @@ enum GeolocationFuzzMethod {
 
 class GeolocationSetting MOZ_FINAL {
 public:
-  GeolocationSetting(const nsString& aOrigin) :
+  explicit GeolocationSetting(const nsString& aOrigin) :
     mFuzzMethod(GEO_ALA_TYPE_DEFAULT),
 #ifdef MOZ_APPROX_LOCATION
     mDistance(0),
diff --git a/dom/html/nsBrowserElement.cpp b/dom/html/nsBrowserElement.cpp
index 32918531093..1418bcb3dca 100644
--- a/dom/html/nsBrowserElement.cpp
+++ b/dom/html/nsBrowserElement.cpp
@@ -35,7 +35,7 @@ class nsBrowserElement::BrowserShownObserver : public nsIObserver
                                              , public nsSupportsWeakReference
 {
 public:
-  BrowserShownObserver(nsBrowserElement* aBrowserElement);
+  explicit BrowserShownObserver(nsBrowserElement* aBrowserElement);
   NS_DECL_ISUPPORTS
   NS_DECL_NSIOBSERVER
   void AddObserver();
diff --git a/dom/ipc/TabChild.cpp b/dom/ipc/TabChild.cpp
index 9212567042d..8bee1836ccf 100644
--- a/dom/ipc/TabChild.cpp
+++ b/dom/ipc/TabChild.cpp
@@ -758,7 +758,7 @@ class TabChild::DelayedDeleteRunnable MOZ_FINAL
     nsRefPtr<TabChild> mTabChild;
 
 public:
-    DelayedDeleteRunnable(TabChild* aTabChild)
+    explicit DelayedDeleteRunnable(TabChild* aTabChild)
       : mTabChild(aTabChild)
     {
         MOZ_ASSERT(NS_IsMainThread());
diff --git a/dom/media/MediaDevices.h b/dom/media/MediaDevices.h
index af18c8639e9..cbacbd086ca 100644
--- a/dom/media/MediaDevices.h
+++ b/dom/media/MediaDevices.h
@@ -24,7 +24,8 @@ struct MediaStreamConstraints;
 class MediaDevices MOZ_FINAL : public DOMEventTargetHelper
 {
 public:
-  MediaDevices(nsPIDOMWindow* aWindow) : DOMEventTargetHelper(aWindow) {}
+  explicit MediaDevices(nsPIDOMWindow* aWindow) :
+    DOMEventTargetHelper(aWindow) {}
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECLARE_STATIC_IID_ACCESSOR(MOZILLA_DOM_MEDIADEVICES_IMPLEMENTATION_IID)
diff --git a/dom/media/MediaPromise.h b/dom/media/MediaPromise.h
index cbff154d622..8578c97190a 100644
--- a/dom/media/MediaPromise.h
+++ b/dom/media/MediaPromise.h
@@ -57,7 +57,7 @@ public:
   typedef RejectValueT RejectValueType;
 
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(MediaPromise)
-  MediaPromise(const char* aCreationSite)
+  explicit MediaPromise(const char* aCreationSite)
     : mCreationSite(aCreationSite)
     , mMutex("MediaPromise Mutex")
   {
@@ -138,7 +138,7 @@ protected:
       RejectValueType mRejectValue;
     };
 
-    ThenValueBase(const char* aCallSite) : mCallSite(aCallSite)
+    explicit ThenValueBase(const char* aCallSite) : mCallSite(aCallSite)
     {
       MOZ_COUNT_CTOR(ThenValueBase);
     }
diff --git a/dom/media/MediaStreamError.h b/dom/media/MediaStreamError.h
index f8a6e5ac02c..13e675cb930 100644
--- a/dom/media/MediaStreamError.h
+++ b/dom/media/MediaStreamError.h
@@ -44,9 +44,9 @@ class MediaMgrError MOZ_FINAL : public nsISupports,
                                 public BaseMediaMgrError
 {
 public:
-  MediaMgrError(const nsAString& aName,
-                const nsAString& aMessage =  EmptyString(),
-                const nsAString& aConstraintName =  EmptyString())
+  explicit MediaMgrError(const nsAString& aName,
+                         const nsAString& aMessage =  EmptyString(),
+                         const nsAString& aConstraintName =  EmptyString())
   : BaseMediaMgrError(aName, aMessage, aConstraintName) {}
 
   NS_DECL_THREADSAFE_ISUPPORTS
diff --git a/dom/media/MediaStreamGraph.h b/dom/media/MediaStreamGraph.h
index 7c8131614ee..cf120e6578e 100644
--- a/dom/media/MediaStreamGraph.h
+++ b/dom/media/MediaStreamGraph.h
@@ -1211,7 +1211,7 @@ public:
   TrackRate GraphRate() const { return mSampleRate; }
 
 protected:
-  MediaStreamGraph(TrackRate aSampleRate)
+  explicit MediaStreamGraph(TrackRate aSampleRate)
     : mNextGraphUpdateIndex(1)
     , mSampleRate(aSampleRate)
   {
diff --git a/dom/media/MediaTaskQueue.h b/dom/media/MediaTaskQueue.h
index ce3827b52cf..439f7b97d74 100644
--- a/dom/media/MediaTaskQueue.h
+++ b/dom/media/MediaTaskQueue.h
@@ -92,7 +92,8 @@ private:
     RefPtr<nsIRunnable> mRunnable;
     bool mForceDispatch;
 
-    TaskQueueEntry(TemporaryRef<nsIRunnable> aRunnable, bool aForceDispatch = false)
+    explicit TaskQueueEntry(TemporaryRef<nsIRunnable> aRunnable,
+                            bool aForceDispatch = false)
       : mRunnable(aRunnable), mForceDispatch(aForceDispatch) {}
   };
 
diff --git a/dom/media/fmp4/SharedDecoderManager.cpp b/dom/media/fmp4/SharedDecoderManager.cpp
index 344f3dfefa0..d59c95450d0 100644
--- a/dom/media/fmp4/SharedDecoderManager.cpp
+++ b/dom/media/fmp4/SharedDecoderManager.cpp
@@ -12,7 +12,7 @@ namespace mozilla {
 class SharedDecoderCallback : public MediaDataDecoderCallback
 {
 public:
-  SharedDecoderCallback(SharedDecoderManager* aManager) : mManager(aManager) {}
+  explicit SharedDecoderCallback(SharedDecoderManager* aManager) : mManager(aManager) {}
 
   virtual void Output(MediaData* aData) MOZ_OVERRIDE
   {
diff --git a/dom/media/gmp-plugin/gmp-test-decryptor.cpp b/dom/media/gmp-plugin/gmp-test-decryptor.cpp
index 60c99f5aae9..dd2e7d06c06 100644
--- a/dom/media/gmp-plugin/gmp-test-decryptor.cpp
+++ b/dom/media/gmp-plugin/gmp-test-decryptor.cpp
@@ -150,9 +150,9 @@ public:
 
 class SendMessageTask : public GMPTask {
 public:
-  SendMessageTask(const string& aMessage,
-                  TestManager* aTestManager = nullptr,
-                  const string& aTestID = "")
+  explicit SendMessageTask(const string& aMessage,
+                           TestManager* aTestManager = nullptr,
+                           const string& aTestID = "")
     : mMessage(aMessage), mTestmanager(aTestManager), mTestID(aTestID) {}
 
   void Run() MOZ_OVERRIDE {
diff --git a/dom/media/gmp-plugin/gmp-test-decryptor.h b/dom/media/gmp-plugin/gmp-test-decryptor.h
index fe9000c611e..efea3f3e8ac 100644
--- a/dom/media/gmp-plugin/gmp-test-decryptor.h
+++ b/dom/media/gmp-plugin/gmp-test-decryptor.h
@@ -14,7 +14,7 @@
 class FakeDecryptor : public GMPDecryptor {
 public:
 
-  FakeDecryptor(GMPDecryptorHost* aHost);
+  explicit FakeDecryptor(GMPDecryptorHost* aHost);
 
   virtual void Init(GMPDecryptorCallback* aCallback) MOZ_OVERRIDE {
     mCallback = aCallback;
diff --git a/dom/media/gmp/GMPChild.cpp b/dom/media/gmp/GMPChild.cpp
index ef652d3c207..aa8057c4ef9 100644
--- a/dom/media/gmp/GMPChild.cpp
+++ b/dom/media/gmp/GMPChild.cpp
@@ -361,7 +361,7 @@ GMPChild::PreLoadLibraries(const std::string& aPluginPath)
 #if defined(XP_MACOSX)
 class MacOSXSandboxStarter : public SandboxStarter {
 public:
-  MacOSXSandboxStarter(GMPChild* aGMPChild)
+  explicit MacOSXSandboxStarter(GMPChild* aGMPChild)
     : mGMPChild(aGMPChild)
   {}
   virtual void Start(const char* aLibPath) MOZ_OVERRIDE {
diff --git a/dom/media/gmp/GMPStorageChild.cpp b/dom/media/gmp/GMPStorageChild.cpp
index e23de602ba8..30d16f27fde 100644
--- a/dom/media/gmp/GMPStorageChild.cpp
+++ b/dom/media/gmp/GMPStorageChild.cpp
@@ -293,7 +293,7 @@ GMPStorageChild::EnumerateRecords(RecvGMPRecordIteratorPtr aRecvIteratorFunc,
 
 class GMPRecordIteratorImpl : public GMPRecordIterator {
 public:
-  GMPRecordIteratorImpl(const InfallibleTArray<nsCString>& aRecordNames)
+  explicit GMPRecordIteratorImpl(const InfallibleTArray<nsCString>& aRecordNames)
     : mRecordNames(aRecordNames)
     , mIndex(0)
   {
diff --git a/dom/media/webm/SoftwareWebMVideoDecoder.h b/dom/media/webm/SoftwareWebMVideoDecoder.h
index 36b345bd15c..8e304723705 100644
--- a/dom/media/webm/SoftwareWebMVideoDecoder.h
+++ b/dom/media/webm/SoftwareWebMVideoDecoder.h
@@ -24,7 +24,7 @@ public:
 
   virtual void Shutdown() MOZ_OVERRIDE;
 
-  SoftwareWebMVideoDecoder(WebMReader* aReader);
+  explicit SoftwareWebMVideoDecoder(WebMReader* aReader);
   ~SoftwareWebMVideoDecoder();
 
 private:
diff --git a/dom/plugins/ipc/PluginModuleChild.h b/dom/plugins/ipc/PluginModuleChild.h
index 312415f7a69..8b502ebd4be 100644
--- a/dom/plugins/ipc/PluginModuleChild.h
+++ b/dom/plugins/ipc/PluginModuleChild.h
@@ -150,7 +150,7 @@ protected:
     virtual bool AnswerGetProfile(nsCString* aProfile) MOZ_OVERRIDE;
 
 public:
-    PluginModuleChild(bool aIsChrome);
+    explicit PluginModuleChild(bool aIsChrome);
     virtual ~PluginModuleChild();
 
     bool CommonInit(base::ProcessHandle aParentProcessHandle,
diff --git a/dom/vr/VRDevice.h b/dom/vr/VRDevice.h
index 514bc901f4e..ac1f8053501 100644
--- a/dom/vr/VRDevice.h
+++ b/dom/vr/VRDevice.h
@@ -222,7 +222,7 @@ public:
   virtual JSObject* WrapObject(JSContext* aCx) MOZ_OVERRIDE;
 
 protected:
-  PositionSensorVRDevice(nsISupports* aParent)
+  explicit PositionSensorVRDevice(nsISupports* aParent)
     : VRDevice(aParent, VRDevice::PositionSensor)
   { }
 
diff --git a/dom/workers/ServiceWorkerClients.h b/dom/workers/ServiceWorkerClients.h
index a1ea870d294..40b32b326f0 100644
--- a/dom/workers/ServiceWorkerClients.h
+++ b/dom/workers/ServiceWorkerClients.h
@@ -28,7 +28,7 @@ public:
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(ServiceWorkerClients)
 
-  ServiceWorkerClients(ServiceWorkerGlobalScope* aWorkerScope);
+  explicit ServiceWorkerClients(ServiceWorkerGlobalScope* aWorkerScope);
 
   already_AddRefed<Promise> GetServiced(ErrorResult& aRv);
   already_AddRefed<Promise> ReloadAll(ErrorResult& aRv);