Firefox bug #733698 workaround

fx733698.js

(function(){
	var FakeTextMetrics,
		proto,
		fontSetterNative,
		measureTextNative,
		fillTextNative,
		strokeTextNative;

	if (
		!window.CanvasRenderingContext2D ||
		!window.TextMetrics ||
		!(proto = window.CanvasRenderingContext2D.prototype) ||
		!proto.hasOwnProperty("font") ||
		!proto.hasOwnProperty("mozTextStyle") ||
		typeof proto.__lookupSetter__ !== "function" || 
		!(fontSetterNative = proto.__lookupSetter__("font"))
	){
		return;		
	}
	
	proto.__defineSetter__("font", function(value){
		try {
			return fontSetterNative.call(this, value);
		} catch (e){
			if (e.name !== 'NS_ERROR_FAILURE'){
				throw e;				
			}
		}
	});

	measureTextNative = proto.measureText;
	FakeTextMetrics = function(){
		this.width = 0;
		this.isFake = true;
		this.__proto__ = window.TextMetrics.prototype;
	};
	proto.measureText = function($0){
		try {
			return measureTextNative.apply(this, arguments);
		} catch (e) {
			if (e.name !== 'NS_ERROR_FAILURE'){
				throw e;				
			} else {
				return new FakeTextMetrics();				
			}
		}
	};

	fillTextNative = proto.fillText;
	proto.fillText = function($0, $1, $2, $3){
		try {
			fillTextNative.apply(this, arguments);
		} catch (e) {
			if (e.name !== 'NS_ERROR_FAILURE'){
				throw e;				
			}
		}
	};

	strokeTextNative = proto.strokeText;
	proto.strokeText = function($0, $1, $2, $3){
		try {
			strokeTextNative.apply(this, arguments);
		} catch (e) {
			if (e.name !== 'NS_ERROR_FAILURE'){
				throw e;			
			}
		}
	};

})();