Emoji Censor от Gilmore Davidson

This add-on lets you embrace your grumpy side by redacting (blacking out) all emoji characters as you browse.

Just click the Emoji Censor icon to turn censoring on or off. While it's on, you'll see a count of how many pesky emoji have been removed from your vision.

The code is open source, and is also available as a web page with audio censoring.