Is this In Thunderbird (extension?) or a Firefox Extension?

I need to know how to activate the 'Firefox' reminder 'option' - it is part of firefox

Sorry, Firefox doesn't include a "reminder" feature.

How about providing a listing of your installed extensions, from Help > Troubleshooting Information.

Yes it does I used it - there is a calendar and you are able to set reminders for any date and even repeat daily, weekly, monthly, annually etc.

Sorry, the Firefox web browser has never had a calendar as a standard feature.

I've been using it for the past couple of years until two days ago

As I asked just over 12 hours ago, how about providing a listing of your installed extensions? It might help us figure out what you installed which added that feature to Firefox.

thanks for your efforts but I got it back - did a google search for firefox reminder and it came right up and I installed it - thanks again

Just to reiterate the the-edmeister's statement that Firefox does not contain a 'reminder' function nor a calendar. It is either a 3rd party extension/plugin or a web service that you are using.

Please make sure you can trust the source of the software before you install anything into your browser, especially if you use the browser, or the machine it is on, for any important tasks (online banking etc.).

This response does not answer the question in any way - I resolved the problem without assistance