This example is built using Babel and Webpack, and so the transpiled bundles have to be built first:
you need to change into the example subdirectory and install all [NodeJS][nodejs] dependencies with npm or yarn:
npm install
You can build the extension using:
npm run build
This creates the source bundles for the WebExtension in the extension subdirectory, and
you can manually install the add-on on Firefox by loading the extension from the
"about:debugging#addons" page.
You can also build the sources and start a new Firefox instance with the add-on installed in one command:
npm run start
To start a webpack instance that automatically rebuilds the add-on when you change the sources, in another shell window, you can run the following npm script:
npm run build:watch
While this npm script is running, any time you edit a file, it will be rebuilt automatically.