Greasy Fork is available in English.
Show metacritic metascore and user ratings on: Bandcamp, Apple Itunes (Music), Amazon (Music,Movies,TV Shows), IMDb (Movies), Google Play (Music, Movies), Steam, Gamespot (PS4, XONE, PC), Rotten Tomatoes, Serienjunkies, BoxOfficeMojo, allmovie.com, fandango.com, Wikipedia (en), themoviedb.org, letterboxd, TVmaze, TVGuide, followshows.com, TheTVDB.com, ConsequenceOfSound, Pitchfork, Last.fm, TVnfo, rateyourmusic.com, GOG, Epic Games Store, save.tv
Tested with Firefox/Greasemonkey and Chrome/Tampermonkey.
Version for Safari: https://openuserjs.org/scripts/cuzi/Show_Metacritic.com_ratings_(Safari)
I develop a similar script for the Rotten Tomatoes score, see cuzi/Show_Rottentomatoes_meter
Supported sites and products:
Screenshot:
If no matching entry on Metacritic.com is found, you can type meta and a search field will appear in the lower left corner.
https://github.com/cvzi/Metacritic-userscript
