It's in the article ...

The flag symbol highlights our activist spirit, signifying a commitment to ‘Reclaim the Internet.’ A symbol of belief, peace, unity, pride, celebration and team spirit—built from the ‘M’ for Mozilla and a pixel that is conveniently displaced to reveal a wink to its iconic Tyrannosaurus rex symbol designed by Shepard Fairey. The flag can transform into a more literal interpretation as its new mascot in ASCII art style, and serve as a rallying cry for our cause.