--- a/xpcom/rust/nsstring/src/lib.rs
+++ b/xpcom/rust/nsstring/src/lib.rs
@@ -979,17 +979,17 @@ impl From<String> for nsCString {
     fn from(s: String) -> nsCString {
         s.into_bytes().into()
     }
 }
 
 // Support for the write!() macro for appending to nsACStrings
 impl fmt::Write for nsACString {
     fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
-        self.append(&nsCString::from(s));
+        self.append(s);
         Ok(())
     }
 }
 
 impl fmt::Display for nsACString {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
         fmt::Display::fmt(&String::from_utf8_lossy(&self[..]), f)
     }
@@ -1097,17 +1097,17 @@ impl<'a> From<&'a String> for nsString {
     }
 }
 
 // Support for the write!() macro for writing to nsStrings
 impl fmt::Write for nsAString {
     fn write_str(&mut self, s: &str) -> Result<(), fmt::Error> {
         // Directly invoke gecko's routines for appending utf8 strings to
         // nsAString values, to avoid as much overhead as possible
-        self.append_utf8(&nsCString::from(s));
+        self.append_utf8(s);
         Ok(())
     }
 }
 
 impl fmt::Display for nsAString {
     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
         fmt::Display::fmt(&String::from_utf16_lossy(&self[..]), f)
     }