Probably due to new webpack default settings outputglobalobject which is window we are seeing this generated inside forge.all.min.,js and forge.min.js now

(window, (function () {

and previously we had this

"undefined"!=typeof self?self:this

which allowed to run node-forge inside web workers.
Possible solution? Apply this to webpack.config.js

module.exports = {
  // ...
  output: {
    globalObject: 'this'
  }
};
output.