he engine can render using <canvas>, <svg> and WebGL.
It runs in canvas. I still don't see the point there, sorry.
For Native Client, atm it is only supported in Chrome. The developpement team for mozilla for sure and Safari, or Opera (I can't remember the exact quote) are not really looking into adding it to their browser.
And it will require you to learn some language like c++, won't it ?
In regards to learning a new language, I think there's a good chunk of middleware that'll let you get away without a lot of c++ knowledge. I believe Unity has confirmed NaCl support in the future, for example.