I\'m planning to write a 3D FPS game, based on WebGL.
Depending on your platform, if your FPS game runs on PC browser with powerful graphics card and CPU, then the best option for you is unity3D.
If your game targets on mobile phone, maybe you could try THREE.js or SceneJS.
And if your time is limited, and your game is a bit sophisticated, I recommend you the LAYABOX, for its complete ecosystem and full of tools, that could save a lot of work. Hope it helps.