There are various ways of testing this, for instance in the case of ‘flatten’ Firefox released it in their Nightly and it did break a top 100 site, that was eno

There are various ways of testing this, for instance in the case of ‘flatten’ Firefox released it in their Nightly and it did break a top 100 site, that was enough to end the debate. https://bugzilla.mozilla.org/show_bug.cgi?id=1443630 https://bugzilla.mozilla.org/show_bug.cgi?id=1443630