There is a hidden one game in Firefox called Unicorn Pong and to play with it you need to know how to approach it.
It seems that it is now fashionable for every browser to have a hidden game. The 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 the hamburger menu (the three horizontal bars) in the upper right, and then click "Customize."
Step 2. In Firefox's “Customize” tab, you'll see a list of available data to configure the toolbar. Click and drag all toolbar items to the right of the “Overflow Menu” except “Flexible Space”.
Step 3. At the bottom of the window will appear the button "Unicorn". Click on it.
Step 4. A Pong game with a small one will appear on the left side of the tab icon unicorn. 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.