I archive this repository and remove the addon from addon stores because I cannot spare my time maintaining the code.
If you want to keep using this addon, feel free to fork or copy source code to build.
To build add-on for Chrome, follow the procedure below.
- If you haven't created PEM file yet, create it by packaging src folder with Chrome browser and rename it from src.pem to key.pem.
 - Copy and paste key.pem into ./src/
 - Zip the contents of src directory by:
 
cd ./src
zip multiwindow_chrome-0.0.x.zip -r ./*
- Upload to Chrome developer site
 
To build add-on for Firefox, follow the procedure below.
- If you haven't installed 
web-extnpm module yet, install it bynpm install -g web-ext - Remove key.pem if it exists under ./src
 - Dispatch build tool
 
web-ext build -s src
- Upload add-on file to AMO