--- a/js/xpconnect/src/Sandbox.cpp
+++ b/js/xpconnect/src/Sandbox.cpp
@@ -635,17 +635,17 @@ const xpc::SandboxCallableProxyHandler x
  * "this" we will instead call it with newThisObj as the this.
  */
 static JSObject*
 WrapCallable(JSContext *cx, HandleObject callable, HandleObject sandboxProtoProxy)
 {
     MOZ_ASSERT(JS::IsCallable(callable));
     // Our proxy is wrapping the callable.  So we need to use the
     // callable as the private.  We put the given sandboxProtoProxy in
-    // an extra slot,, and our call() hook depends on that.
+    // an extra slot, and our call() hook depends on that.
     MOZ_ASSERT(js::IsProxy(sandboxProtoProxy) &&
                js::GetProxyHandler(sandboxProtoProxy) ==
                  &xpc::sandboxProxyHandler);
 
     RootedValue priv(cx, ObjectValue(*callable));
     JSObject *obj = js::NewProxyObject(cx, &xpc::sandboxCallableProxyHandler,
                                        priv, nullptr);
     if (obj) {