Using "requireCordovaModule" to load non-cordova module "fs" is not supported. Instead, add this module to your dependencies and use regular "require" to load it code example

Example: Using "requireCordovaModule" to load non-cordova module "xcode" is not supported

Install xcode: npm i xcode --save-dev
Edit the plugin file locally plugins/cordova-plugin-firebase/scripts/ios/helper.js
Add var xcode = require("xcode"); on top
Then in the same file, just remove this line var xcode = context.requireCordovaModule("xcode");. You must find two occurrence of this line.