My mentality is to make the website usable without JS for most people (with the reasonable effort of installing FF or Chrome at most), then use as simple and co

My mentality is to make the website usable without JS for most people (with the reasonable effort of installing FF or Chrome at most), then use as simple and compatible JS as possible if needed. Thus, old-style DOM fiddling isn't the first choice - and if we're talking very old browsers, it was also tricky to get right due to all the incompatibilities. Why you think something would be broken when a polyfill is used as fallback, I don't know.