Why does it say "Your browser does not support WebGL?"
What browser do you recommend?
This list will likely change (and hopefully become irrelevant) as the technology becomes more widespread and improves. But at the time of this writing, my un-scientific survey of various devices and browsers ranks them in the following order:
Opera. Yes, that's right - I've found Opera gives me the best, smoothest framerate, even better than Chrome. (On desktops and laptops anyway. On mobile devices, Chrome is still king.)
Google Chrome. This is generally considered the browser of choice for most WebGL developers.
Firefox. Also very good. Depending on your hardware/OS, I tend to find Firefox's framerate a little less stable. It seems to work best in full-screen mode. Also I find that Firefox can be slowed down by other open tabs or windows, especially if they've been open for a long time. Close all your browser windows and restart Firefox fresh for best results.
Safari. At the time of this writing, Safari is decent at WebGL, but slower than the above browsers. Look for big improvements with the next OS release when Apple supports WebGL officially.
Additionally, Safari does not support the OGG sound format. Unfortunately both MP3 and M4A formats do not allow for perfectly seamless music looping and add greater latency when playing sound effects.
Internet Explorer 11. ONLY IE11+ supports WebGL, no earlier versions will work. In my experience, IE11 performance ranges from very, very fast to very, very slow. On some computers, IE will decide to use software emulaton, in which case the game will run very slowly. If you MUST use IE11, and it's performing poorly, use the lowest performance settings in the game and try playing in a smaller window rather than full screen.
It's also worth noting that IE does not yet support the new Web Audio API. This means sounds and music will be much more crude in IE11 than other browsers.
Can I play on mobile devices?
There isn't yet a way to play the game with touch input, so no. It is planned for the future however. Watch the blog for updates.
Note that you CAN watch replays on mobile devices/browsers that support WebGL!
I have a recommended browser and a desktop/laptop computer but it still says WebGL is unsupported.
Some devices simply have outdated 3D video cards and/or poor drivers. Check that you have all the latest OS and driver updates for your system. With Chrome, you can enter chrome://gpu into the address bar, which might tell you why WebGL isn't working on your device.