diff --git a/mozilla/string/obsolete/nsString.h b/mozilla/string/obsolete/nsString.h
index 3b097d70adc..0f6d884fe86 100644
--- a/mozilla/string/obsolete/nsString.h
+++ b/mozilla/string/obsolete/nsString.h
@@ -544,6 +544,8 @@ public:
     char mBuffer[kDefaultStringSize];
 };
 
+NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsCAutoString, char)
+
 /**
  * A helper class that converts a UCS2 string to UTF8
  */
diff --git a/mozilla/string/obsolete/nsString2.h b/mozilla/string/obsolete/nsString2.h
index 5f11ea6b585..6b9b906618d 100644
--- a/mozilla/string/obsolete/nsString2.h
+++ b/mozilla/string/obsolete/nsString2.h
@@ -620,6 +620,8 @@ public:
     char mBuffer[kDefaultStringSize<<eTwoByte];
 };
 
+NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsAutoString, PRUnichar)
+
 class NS_COM NS_ConvertASCIItoUCS2
       : public nsAutoString
     /*
diff --git a/mozilla/xpcom/ds/nsString.h b/mozilla/xpcom/ds/nsString.h
index 3b097d70adc..0f6d884fe86 100644
--- a/mozilla/xpcom/ds/nsString.h
+++ b/mozilla/xpcom/ds/nsString.h
@@ -544,6 +544,8 @@ public:
     char mBuffer[kDefaultStringSize];
 };
 
+NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsCAutoString, char)
+
 /**
  * A helper class that converts a UCS2 string to UTF8
  */
diff --git a/mozilla/xpcom/ds/nsString2.h b/mozilla/xpcom/ds/nsString2.h
index 5f11ea6b585..6b9b906618d 100644
--- a/mozilla/xpcom/ds/nsString2.h
+++ b/mozilla/xpcom/ds/nsString2.h
@@ -620,6 +620,8 @@ public:
     char mBuffer[kDefaultStringSize<<eTwoByte];
 };
 
+NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsAutoString, PRUnichar)
+
 class NS_COM NS_ConvertASCIItoUCS2
       : public nsAutoString
     /*
diff --git a/mozilla/xpcom/string/obsolete/nsString.h b/mozilla/xpcom/string/obsolete/nsString.h
index 3b097d70adc..0f6d884fe86 100644
--- a/mozilla/xpcom/string/obsolete/nsString.h
+++ b/mozilla/xpcom/string/obsolete/nsString.h
@@ -544,6 +544,8 @@ public:
     char mBuffer[kDefaultStringSize];
 };
 
+NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsCAutoString, char)
+
 /**
  * A helper class that converts a UCS2 string to UTF8
  */
diff --git a/mozilla/xpcom/string/obsolete/nsString2.h b/mozilla/xpcom/string/obsolete/nsString2.h
index 5f11ea6b585..6b9b906618d 100644
--- a/mozilla/xpcom/string/obsolete/nsString2.h
+++ b/mozilla/xpcom/string/obsolete/nsString2.h
@@ -620,6 +620,8 @@ public:
     char mBuffer[kDefaultStringSize<<eTwoByte];
 };
 
+NS_DEF_DERIVED_STRING_OPERATOR_PLUS(nsAutoString, PRUnichar)
+
 class NS_COM NS_ConvertASCIItoUCS2
       : public nsAutoString
     /*