I started by googling the topic and coming upon this article: https://blog.mozilla.org/addons/2014/06/05/how-to-develop-firefox-extension/
It then took me to this link that had a whole bunch of instructions and tutorials on how to develop the plugin: https://developer.mozilla.org/en-US/Add-ons/SDK
My goal for this plugin was to be able to press a button to display the total number of words completed on duolingo.com. As of April 26th, 2016 duolingo doesn’t show the total number/count of words that you have completed in it. For me that count was over 1000 so it wasn’t practical for me to know how many words I have in my vocabulary. The completed words are displayed on this link when you are logged in: https://www.duolingo.com/words
In order to install jpm, node.js had to be installed first. Then the following command was run in the command prompt: npm install jpm
If you try running a non-signed extension in Firefox it’s going to display an error and not let you install that extension. So API credentials need to be created on developer.mozilla.com. You will have to create a Mozilla account before you do that.
Once any modification is made to the plugin during development I use the following command to see the new functionality: jpm run
I’m going to try to use this: https://developer.mozilla.org/en-US/Add-ons/SDK/High-Level_APIs/page-worker
Then I’m going to count the rows somehow.