step 1:
install dependencies.
step 2:
run npm run start
step 3:
in another terminal, run ./node_modules/.bin/web-ext run -s build.
difference in chrome-extension-webpack-boilerplate
even though web-ext will automatically reload your extension into firefox, but it won't reload your web page,
you have to reload the page manually. there is hot-reload in the chrome-extension-webpack-boilerplate,
but i cant make it work in firefox, so if you can solve the problem, feel free to submit a pr.