HTMLCanvasElement.mozFetchAsStream()

Save to disk with mozFetchAsStream (Chrome context only)

This technique also converts it to ico, however it will not work in Windows XP as WinXP cannot convert from PNG to ICO. It saves to the desktop it uses FileUtils.jsm. Also uses NetUtil.jsm

var canvas = document.getElementById("canvas");
var d = canvas.width;
ctx = canvas.getContext("2d");
ctx.beginPath();
ctx.moveTo(d / 2, 0);
ctx.lineTo(d, d);
ctx.lineTo(0, d);
ctx.closePath();
ctx.fillStyle = "yellow";
ctx.fill();

    var netutilCallback = function() {
        return function(result) {
           if (!Components.isSuccessCode(result)) {               
              alert('FAILED to create icon');
           } else {
               alert('succesfully made');
           }
        };
    }

    var mfasCallback = function(iconName) {
        return function(inStream) {
           var file = FileUtils.getFile("Desk", [iconName + ".ico"]);
           var outStream = FileUtils.openFileOutputStream(file);
           Cu.import("resource://gre/modules/NetUtil.jsm");
           NetUtil.asyncCopy(inStream, outStream, netutilCallback());
        }
    }

canvas.mozFetchAsStream(mfasCallback('myIcon'), 'image/vnd.microsoft.icon');