DOM nodes added by extensions cause failure

[alexgagnon]

Hi, it looks like there are cases where DOM nodes being added by extensions cause the polyfill to choke. I'm my specific case it's using Windows 11, Firefox, Grammarly desktop, and a website built using a common pattern of hiding the body element until the polyfill has finished executing. I imagine this should probably be handled since website visitors would have no understanding as to why they just see an empty page. I can take a look at doing a PR if that's the direction the maintainers want to take.