There is one secret game on Firefox called Unicorn Pong and to play with it you need to know how to approach it.
It seems to be all the rage now program browsing to have a hidden game. Chrome has one game with the dinosaur Dino, the Edge surfs and Firefox plays with Unicorn Pong.
Of course you can also play with Firefox Unicorn. Let's see how….
Step 1. First, open Firefox. Click on menu hamburger (the three horizontal lines) on the top right, and then click "Customize".
Step 2. In Firefox's “Customize” tab, you'll see a list of items available for configuring the toolbar. Click and drag all toolbar items to the right of the “Overflow Menu” except “Flexible space” (Flexible Space).
Step 3. The "Unicorn" button will appear at the bottom of the window. Click on it.
Step 4. A Pong game with a small unicorn icon will appear on the left side of the tab. In this version of the game, the "Flexible Space" box serves as a Pong racket, and the unicorn icon is the ball.
To play, simply use the left and right arrow keys on your keyboard to move the UP flexible space so that the unicorn does not pass through it. The lower Pong packs are automatically handled by the game.
If you lose and want to play again, just double-click the Unicorn button.
When the game is finished, click "Reset Defaults" to reset all the items you went to in the Popup menu with Step 2.