I made this extension not knowing there are a lot of extensions like it lol, but mine is the most stable and recent. My extension is the only one that displays both the Critic score AND the Audience score. It's also the only one that displays the score's associated picture (splat, fresh, etc.), and in a way that is unobtrusive. It's also updated daily with my own software and database, so scores are accurate!
Let me know what you think, suggestions appreciated.