Enable HTML Minification

Global

    public class Global : UmbracoApplication
    {
        protected override void OnApplicationStarting(object sender, EventArgs e)
        {
            GlobalFilters.Filters.Add(new RemoveHtmlWhitespaceFilterAttribute());
            base.OnApplicationStarting(sender, e);
        }
    }

RemoveHtmlWhitespaceFilterAttribute

    public class RemoveHtmlWhitespaceFilterAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            var response = filterContext.HttpContext.Response;

            response.Filter = new ModifyOutputFilter(response.Filter, s =>
            {
                if (I2GSettings.Instance.EnableMinification)
                {
                    s = Regex.Replace(s, @"\s+", " ");
                    s = Regex.Replace(s, @"\s*\n\s*", "\n");
                    s = Regex.Replace(s, @"\s*\>\s*\<\s*", "><");
                    s = Regex.Replace(s, @"<!--(.*?)-->", ""); //Remove comments

                    // single-line doctype must be preserved 
                    var firstEndBracketPosition = s.IndexOf(">", StringComparison.Ordinal);
                    if (firstEndBracketPosition >= 0)
                    {
                        s = s.Remove(firstEndBracketPosition, 1);
                        s = s.Insert(firstEndBracketPosition, ">");
                    }
                }

                return s;
            });
        }
    }