Once installed, users go to the Reaction Packs website to choose which pack they want to use.
All the reactions are the same - 'like', 'love', 'haha' and so on - except the pictures are replaced with whatever you want.
Currently, users can choose from a fun Pokémon pack or a surreal Donald Trump pack, but there should be many more in future.
With a bit of photoshop action, it's possible to make your own packs, filled with anything you want. There's hundreds of similarly divisive politicians out there who could soon be taking pride of place in your Facebook feed.
Obviously, if other Facebook users don't have the extension, they won't see the custom reactions. So there's no need to worry about offending a colleague by putting a picture of a smiling Donald Trump below their latest status.