On firefox 70 using webpack I am developing the following HTML/CSS theme (on the branch occuring the issue) https://github.com/ellakcy/admin-theme/tree/dev

And Using the following webpack configuration:

const path = require('path');
const nodeExternals=require('webpack-node-externals');

module.exports = {
    entry: [
       __dirname+"/src/js/panel.js",
    ],
    output: {
      path: __dirname+'/www',
      publicPath: '/',
      filename: 'panel.js'
    },
    devtool: 'sourcemaps',
    module: