The web extension is just a wrapper around lesspass-pure on npm
node --version: v10.15.0 npm --version: v6.4.1
untar src and install dependencies
cd packages/lesspass-web-extension/
npm install && npm run build
cd extension
find . -type f -exec md5sum {} \; | md5sum
cd packages/lesspass-pure/
npm install && npm run build
md5sum dist/lesspass.min.js