I've tested on both Firefox and Chrome but once I've marked a manga chapter as read it becomes locked. Or vice versa if I mark a chapter as unread then it's locked and I can no longer change the icon back to read. I can refresh the page and change it but I can only change it once before it locks again and each chapter acts independently. For example I can mark chapter 1 , 2 , and 3 as read but will not be able to interact and change the icon for any of those chapters until I refresh. Not a huge bug but there we go.