anyone know how to debug chrome extention independently (not using google chrome)

[sh3dow]

Assuming you don't want a standalone debugger [I don't think there is one for debugging chrome extensions without using chrome] but a debugger that leverage chrome to debug the JavaScript code.

there is webstorm from jetbrains which has a very good debugger that leverage any Chromium-based browsers to debug javascript
https://www.jetbrains.com/help/webstorm/debugging-javascript-in-chrome.html
https://blog.jetbrains.com/webstorm/2018/01/debugging-javascript-with-webstorm-2017-3/

there is also Chrome Debugging for VS Code
https://code.visualstudio.com/blogs/2016/02/23/introducing-chrome-debugger-for-vs-code

Also you can arm your chrome devtools with extensions to enhance your experience and improve chrome developer tools