See IMDB, RottenTomatoes, and Metacritic ratings on Letterboxd
This chrome extension will fetch and embed IMDB, Rotten Tomatoes, and Metacritic ratings right onto the Letterboxd film page. You can also show and hide ratings right on the chrome extension.
Source code is at https://github.com/EKarton/More-Ratings-on-Letterboxd. Open contributions to the source code are welcome. Thank you!