IMDb SeenList by Sorin

IMDb Seen List is a browser extension that helps users of IMDb.com easily keep track of the movies and shows they've already watched.

The extension allows you to designate one of your own lists as the "Seen List." From there, you can add or remove titles in the same way you manage your IMDb watchlist.

Never again ask yourself, "Have I seen this already?" while browsing IMDb.