Count closed tabs?

I’d like to develop a ‘Count Closed Tabs’ addin/plugin for Firefox.

The idea is that I’d like to gamify the process of cleaning up after my online excursions. The metric of number of closed tabs seems like a reasonable proxy for how well I did for the day.

Would this be technically feasible? Where should I start? I have never developed a plugin before.
thank you so much!

There is a tabClose event, so what you want should be easy. As always, the work is likely to be in presenting the information and tweaking the addon behaviour (eg. resetting counts).

Thank you so much Lithopsian. It looks like from [1] that I can use pure JS for this plugin, since the tabs api [2] is a top-level api, right? Later on, I am not sure if the new Chrome-like way [3] will deprecate the JS code? Or will JS still be supported?
Anne

1.[]Main page has debugging , etiequette, performance etc info on how to do a plugin ; ; ; X.Add-ons - Mozilla | MDN ;; https://developer.mozilla.org/en-US/Add-ons

2.[]JavaScript Examples and details about specifially the tab api ; ; This is in the top-level api, so XUL is not required. ; ; X.tabs - Mozilla | MDN ;; https://developer.mozilla.org/en-US/Add-ons/SDK/High-Level_APIs/tabs

3.[] NEW way ; ; ;similar? notify-link-clicks ; it has an injected code into all pages, and the background-script.js that listens to all the pages ; ; X.Example WebExtensions - Mozilla | MDN ;; https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Examples