diff --git a/editor/composer/nsComposerCommands.h b/editor/composer/nsComposerCommands.h
index 90325f419802..37817736c4d1 100644
--- a/editor/composer/nsComposerCommands.h
+++ b/editor/composer/nsComposerCommands.h
@@ -55,7 +55,7 @@ public:                                                 \
 class nsBaseStateUpdatingCommand : public nsBaseComposerCommand
 {
 public:
-  nsBaseStateUpdatingCommand(nsIAtom* aTagName);
+  explicit nsBaseStateUpdatingCommand(nsIAtom* aTagName);
 
   NS_DECL_ISUPPORTS_INHERITED
 
@@ -80,7 +80,7 @@ protected:
 class nsStyleUpdatingCommand : public nsBaseStateUpdatingCommand
 {
 public:
-  nsStyleUpdatingCommand(nsIAtom* aTagName);
+  explicit nsStyleUpdatingCommand(nsIAtom* aTagName);
            
 protected:
 
@@ -111,7 +111,7 @@ protected:
 class nsListCommand : public nsBaseStateUpdatingCommand
 {
 public:
-  nsListCommand(nsIAtom* aTagName);
+  explicit nsListCommand(nsIAtom* aTagName);
 
 protected:
 
@@ -125,7 +125,7 @@ protected:
 class nsListItemCommand : public nsBaseStateUpdatingCommand
 {
 public:
-  nsListItemCommand(nsIAtom* aTagName);
+  explicit nsListItemCommand(nsIAtom* aTagName);
 
 protected:
 
diff --git a/editor/composer/nsEditorSpellCheck.cpp b/editor/composer/nsEditorSpellCheck.cpp
index 80dfc9ab61f1..a4b665a76752 100644
--- a/editor/composer/nsEditorSpellCheck.cpp
+++ b/editor/composer/nsEditorSpellCheck.cpp
@@ -50,7 +50,7 @@ class UpdateDictionnaryHolder {
   private:
     nsEditorSpellCheck* mSpellCheck;
   public:
-    UpdateDictionnaryHolder(nsEditorSpellCheck* esc): mSpellCheck(esc) {
+    explicit UpdateDictionnaryHolder(nsEditorSpellCheck* esc): mSpellCheck(esc) {
       if (mSpellCheck) {
         mSpellCheck->BeginUpdateDictionary();
       }
diff --git a/editor/txmgr/nsTransactionItem.h b/editor/txmgr/nsTransactionItem.h
index 68fba80483b3..7c811158ef90 100644
--- a/editor/txmgr/nsTransactionItem.h
+++ b/editor/txmgr/nsTransactionItem.h
@@ -25,7 +25,7 @@ class nsTransactionItem MOZ_FINAL
 
 public:
 
-  nsTransactionItem(nsITransaction *aTransaction);
+  explicit nsTransactionItem(nsITransaction *aTransaction);
   NS_METHOD_(MozExternalRefCountType) AddRef();
   NS_METHOD_(MozExternalRefCountType) Release();