Source Maps not when using debugger with npm start

[Anzumana]

I am not sure why but when i run the debugger inside firefox, the sources from webpack are being mapped correctly to the source files.

But when i do the same running the debugger using npm start
i get this

Is there something i would have to configure additionally ?
In case you want to replicate
the project that i am using can be found https://github.com/Anzumana/thecorevisualizer.

The project was created using the react cli just fyi.

[loganfsmyth]

We've moved development of the debugger inside the Mozilla repository so the standalone localhost debugger is no longer supported.