To add translations for a new language copy _locales/en_CA/messages.json to a new folder with the proper language code inside _locales then follow this guide to create a pull request.
Only the "message" values need to be translated, the "description" is just to give some context to translators.
Related Links:
- https://developer.mozilla.org/Add-ons/WebExtensions/API/i18n/Locale-Specific_Message_reference
- https://developer.mozilla.org/Add-ons/WebExtensions/Internationalization
Run npm run dev to build the dev build then npm run webext to start a Firefox instance with the addon
Run npm run prod to build the minified production build