Start by installing gulp and other build dependencies by running:
npm install --only=dev
Then replace the applications.gecko.id key in /shared/manifest.json with either your own key or a string in email format (e.g. [email protected])
Finally build the packages by running in the root directory:
gulp build
The packages will be created in /dist/, ready for submission as an extension, and the debug folders will be updated.
To temporarily install the extension on Firefox, you need to first enter the "Debug Addons" page, available through the menu on the Addons page. Then click "Load Temporary Addon", and point to /dist/webext/debug and click on any file in the directory to load the extension.
To temporarily install the extension on Chrome, you can load /dist/chrome/debug as an unpacked extension