Proper way to detect WebGL support?

Question

I am attempting to detect WebGL support across multiple browsers and I've encountered the following scenario. The current version of Firefox appears to report positive support using the following check, even when the visitor's video card is black-listed and/or WebGL is disabled:

if (window.WebGLRenderingContext) {
    // This is true in Firefox under certain circumstances,
    // even when WebGL is disabled...
}

I've tried instructing my users to enable WebGL using the following steps. This has worked in some cases, but not always. Obviously, this is not something I can request of the general public:

1. Type about:config in Firefox’s address bar
2. To enable WebGL, set webgl.force-enabled to true

This has led me to create my own method for detecting support, which uses jQuery to inject a canvas element to detect support. This pulls on a number of techniques I found in various WebGL libraries and plugins. The trouble is, it is extremely difficult to test (any comments on whether the link below works for you are much appreciated!). To make this an objective question, I would like to know if there's a universally accepted way to detect WebGL support across all browsers.

TEST URL:

http://jsfiddle.net/Jn49q/5/

Answer 1

[Oct 2014] I've updated modernizrs example to match their current implementation, which is a cleaned up version from http://get.webgl.org/ further below.

Modernizr does,

var canvas;
var ctx;
var exts;

try {
  canvas = createElement('canvas');
  ctx = canvas.getContext('webgl') || canvas.getContext('experimental-webgl');
  exts = ctx.getSupportedExtensions();
}
catch (e) {
  return;
}

if (ctx !== undefined) {
  Modernizr.webglextensions = new Boolean(true);
}

for (var i = -1, len = exts.length; ++i < len; ){
  Modernizr.webglextensions[exts[i]] = true;
}

canvas = undefined;

Chromium points to http://get.webgl.org/ for the canonical support implementation,

try { gl = canvas.getContext("webgl"); }
catch (x) { gl = null; }

if (gl == null) {
    try { gl = canvas.getContext("experimental-webgl"); experimental = true; }
    catch (x) { gl = null; }
}