createScriptLoader's onLoad fails from time to time with FF

[jchatard]

Describe the bug

In Firefox-based browsers, the onload callback of createScriptLoader is not fired systematically.

It works perfectly in Chrome, but it fails in Firefox.

I've set up a reproduction using Cypress, which allows testing the behavior in different browsers.

Instructions are in the README.

Minimal Reproduction Link

https://github.com/jchatard/script-loader-ff