_isDuffSafari = function () {
	var safari =
		navigator.userAgent.indexOf('Safari') !== -1 &&
		navigator.userAgent.indexOf('Chrome') === -1 &&
		navigator.userAgent.indexOf('Opera') === -1;

	if (!safari) {
		return false;
	}

	var version = navigator.userAgent.match(/AppleWebKit\/(\d+\.\d+)/);
	if (version && version.length > 1 && version[1] * 1 < 603.1) {
		return true;
	}

	return false;
}
Older versions of Safari (prior to tech preview 18) don't support the
download option required.

@return {Boolean} `true` if old Safari