Just like Chrome, Mozilla now supports playback of PC games right on your browser. Mozilla has teamed up with Humble to come up 8 such games available right in your browser. All of these games are based on asm.js and WebGL technology to make it available right on your browser and doesn't require any software or plugin download.
Just today morning as I opened Firefox, I was surprised to see this on the Start page. Humble has ported 8 games starting with Humble Mozilla Bundle, Super Hexagon, Aaaa! for the Awesome, Osmos, Zen Bound 2, Dustforce DX, Voxatron and FTL: Advanced Edition. The Humble Bundle homepage suggests that Democracy 3 game is available for playing at $8. These games are also compatible with Chrome browser as well.
Here is the hands-on with Humble Mozilla Bundle game