diff --git a/string/public/nsSharableString.h b/string/public/nsSharableString.h
index e28e62ff106d..dc45249b9c4c 100644
--- a/string/public/nsSharableString.h
+++ b/string/public/nsSharableString.h
@@ -72,6 +72,13 @@ class NS_COM nsSharableString
           return *this;
         }
 
+      // copy-assignment operator.  I must define my own if I don't want the compiler to make me one
+      self_type& operator=( const self_type& aReadable )
+        {
+          Assign(aReadable);
+          return *this;
+        }
+
       /**
        * The |Adopt| method assigns a raw, null-terminated, character
        * buffer to this string object by transferring ownership of that
@@ -134,6 +141,13 @@ class NS_COM nsSharableCString
           return *this;
         }
 
+      // copy-assignment operator.  I must define my own if I don't want the compiler to make me one
+      self_type& operator=( const self_type& aReadable )
+        {
+          Assign(aReadable);
+          return *this;
+        }
+
       /**
        * The |Adopt| method assigns a raw, null-terminated, character
        * buffer to this string object by transferring ownership of that
diff --git a/string/public/nsXPIDLString.h b/string/public/nsXPIDLString.h
index ecb7defe15ae..43a3fbaa1176 100644
--- a/string/public/nsXPIDLString.h
+++ b/string/public/nsXPIDLString.h
@@ -170,6 +170,7 @@ class NS_COM nsXPIDLString
         }
 #endif
 
+      // |operator=| does not inherit, so we must provide it again
       self_type&
       operator=( const abstract_string_type& aReadable )
         {
@@ -177,6 +178,14 @@ class NS_COM nsXPIDLString
           return *this;
         }
 
+      // copy-assignment operator.  I must define my own if I don't want the compiler to make me one
+      self_type&
+      operator=( const self_type& aReadable )
+        {
+          Assign(aReadable);
+          return *this;
+        }
+
       /**
        * This is an override of a non-virtual function on
        * |nsSharableString|.  This override is not necessary, but it can
@@ -282,6 +291,7 @@ class NS_COM nsXPIDLCString
         }
 #endif
 
+      // |operator=| does not inherit, so we must provide it again
       self_type&
       operator=( const abstract_string_type& aReadable )
         {
@@ -289,6 +299,14 @@ class NS_COM nsXPIDLCString
           return *this;
         }
 
+      // copy-assignment operator.  I must define my own if I don't want the compiler to make me one
+      self_type&
+      operator=( const self_type& aReadable )
+        {
+          Assign(aReadable);
+          return *this;
+        }
+
       /**
        * This is an override of a non-virtual function on
        * |nsSharableCString|.  This override is not necessary, but it can
diff --git a/xpcom/string/public/nsSharableString.h b/xpcom/string/public/nsSharableString.h
index e28e62ff106d..dc45249b9c4c 100644
--- a/xpcom/string/public/nsSharableString.h
+++ b/xpcom/string/public/nsSharableString.h
@@ -72,6 +72,13 @@ class NS_COM nsSharableString
           return *this;
         }
 
+      // copy-assignment operator.  I must define my own if I don't want the compiler to make me one
+      self_type& operator=( const self_type& aReadable )
+        {
+          Assign(aReadable);
+          return *this;
+        }
+
       /**
        * The |Adopt| method assigns a raw, null-terminated, character
        * buffer to this string object by transferring ownership of that
@@ -134,6 +141,13 @@ class NS_COM nsSharableCString
           return *this;
         }
 
+      // copy-assignment operator.  I must define my own if I don't want the compiler to make me one
+      self_type& operator=( const self_type& aReadable )
+        {
+          Assign(aReadable);
+          return *this;
+        }
+
       /**
        * The |Adopt| method assigns a raw, null-terminated, character
        * buffer to this string object by transferring ownership of that
diff --git a/xpcom/string/public/nsXPIDLString.h b/xpcom/string/public/nsXPIDLString.h
index ecb7defe15ae..43a3fbaa1176 100644
--- a/xpcom/string/public/nsXPIDLString.h
+++ b/xpcom/string/public/nsXPIDLString.h
@@ -170,6 +170,7 @@ class NS_COM nsXPIDLString
         }
 #endif
 
+      // |operator=| does not inherit, so we must provide it again
       self_type&
       operator=( const abstract_string_type& aReadable )
         {
@@ -177,6 +178,14 @@ class NS_COM nsXPIDLString
           return *this;
         }
 
+      // copy-assignment operator.  I must define my own if I don't want the compiler to make me one
+      self_type&
+      operator=( const self_type& aReadable )
+        {
+          Assign(aReadable);
+          return *this;
+        }
+
       /**
        * This is an override of a non-virtual function on
        * |nsSharableString|.  This override is not necessary, but it can
@@ -282,6 +291,7 @@ class NS_COM nsXPIDLCString
         }
 #endif
 
+      // |operator=| does not inherit, so we must provide it again
       self_type&
       operator=( const abstract_string_type& aReadable )
         {
@@ -289,6 +299,14 @@ class NS_COM nsXPIDLCString
           return *this;
         }
 
+      // copy-assignment operator.  I must define my own if I don't want the compiler to make me one
+      self_type&
+      operator=( const self_type& aReadable )
+        {
+          Assign(aReadable);
+          return *this;
+        }
+
       /**
        * This is an override of a non-virtual function on
        * |nsSharableCString|.  This override is not necessary, but it can