See this AMO search for "Calendar" addons for Firefox.

Thank you for your reply but I'm sorry to say, it is not what I am looking for. All those posts relate to time management which is not what I want to focus on. I want a system to quickly record tasks that arise and/or are outstanding, to then categorize them, arranging them into types, e.g; times, work schedules, type of activity, priority etc. and then to schedule to time management later but time management is not the priority, the priority is to capture a "To do List", then to post them to various categories of type and requirement etc. Also a list of 'goals', again to be split into categories. Thank you for your help, time and effort.