--- a/widget/nsIWidget.h
+++ b/widget/nsIWidget.h
@@ -239,17 +239,17 @@ struct nsIMEUpdatePreference {
       NOTIFY_CHANGES_CAUSED_BY_COMPOSITION
   };
 
   nsIMEUpdatePreference()
     : mWantUpdates(DEFAULT_CONDITIONS_OF_NOTIFYING_CHANGES)
   {
   }
 
-  nsIMEUpdatePreference(Notifications aWantUpdates)
+  explicit nsIMEUpdatePreference(Notifications aWantUpdates)
     : mWantUpdates(aWantUpdates | DEFAULT_CONDITIONS_OF_NOTIFYING_CHANGES)
   {
   }
 
   void DontNotifyChangesCausedByComposition()
   {
     mWantUpdates &= ~DEFAULT_CONDITIONS_OF_NOTIFYING_CHANGES;
   }
@@ -364,17 +364,17 @@ struct IMEState {
      * Web contents can specify this value by |ime-mode: inactive;|.
      */
     CLOSED
   };
   Open mOpen;
 
   IMEState() : mEnabled(ENABLED), mOpen(DONT_CHANGE_OPEN_STATE) { }
 
-  IMEState(Enabled aEnabled, Open aOpen = DONT_CHANGE_OPEN_STATE) :
+  explicit IMEState(Enabled aEnabled, Open aOpen = DONT_CHANGE_OPEN_STATE) :
     mEnabled(aEnabled), mOpen(aOpen)
   {
   }
 };
 
 struct InputContext {
   InputContext() : mNativeIMEContext(nullptr) {}
 
@@ -447,18 +447,18 @@ struct InputContextAction {
             mCause == CAUSE_MOUSE);
   }
 
   InputContextAction() :
     mCause(CAUSE_UNKNOWN), mFocusChange(FOCUS_NOT_CHANGED)
   {
   }
 
-  InputContextAction(Cause aCause,
-                     FocusChange aFocusChange = FOCUS_NOT_CHANGED) :
+  explicit InputContextAction(Cause aCause,
+                              FocusChange aFocusChange = FOCUS_NOT_CHANGED) :
     mCause(aCause), mFocusChange(aFocusChange)
   {
   }
 };
 
 /**
  * Size constraints for setting the minimum and maximum size of a widget.
  * Values are in device pixels.
@@ -505,17 +505,17 @@ enum IMEMessage MOZ_ENUM_TYPE(int8_t)
   REQUEST_TO_COMMIT_COMPOSITION,
   // Request to cancel current composition to IME
   // (some platforms may not support)
   REQUEST_TO_CANCEL_COMPOSITION
 };
 
 struct IMENotification
 {
-  IMENotification(IMEMessage aMessage)
+  MOZ_IMPLICIT IMENotification(IMEMessage aMessage)
     : mMessage(aMessage)
   {
     switch (aMessage) {
       case NOTIFY_IME_OF_SELECTION_CHANGE:
         mSelectionChangeData.mCausedByComposition = false;
         break;
       case NOTIFY_IME_OF_TEXT_CHANGE:
         mTextChangeData.mStartOffset = 0;

--- a/widget/xpwidgets/GfxInfoCollector.h
+++ b/widget/xpwidgets/GfxInfoCollector.h
@@ -24,17 +24,17 @@ class MOZ_STACK_CLASS InfoObject
 
   public:
   void DefineProperty(const char *name, int value);
   void DefineProperty(const char *name, nsAString &value);
   void DefineProperty(const char *name, const char *value);
 
   private:
   // We need to ensure that this object lives on the stack so that GC sees it properly
-  InfoObject(JSContext *aCx);
+  explicit InfoObject(JSContext *aCx);
   InfoObject(InfoObject&);
 
   JSContext *mCx;
   JS::Rooted<JSObject*> mObj;
   bool mOk;
 };
 
 /*