Letterboxd Extras is a subscription-based extension for Firefox that enriches the user experience on the popular movie tracking site, Letterboxd. This add-on introduces a variety of additional features, including the ability to view film ratings from multiple external sources such as IMDb, Rotten Tomatoes, and Metacritic. Users can access additional rankings from renowned lists, such as the top 1000 films according to 'They Shoot Pictures, Don't They?' and the BFI Sight and Sound top 250. It also provides an info box for people pages, displaying essential information such as birth dates and years active.

Moreover, Letterboxd Extras enhances the details tabs by including budget and box office figures for films, as well as displaying the MPA rating. Users can easily view the full wide release date and the film duration, which is converted to hours and minutes when hovered over. The search functionality can be customized to filter results specifically to films, making it easier to navigate through the extensive movie database.