@ShadowWizardLoveZelda Half (not all) of the blame can fall on the browser vendor, however. If a given browser doesn't support something that other browsers have supported for multiple years, then part of the blame does fall on the vendor - as an example, think of the days of IE in the late 2000s/early 2010s. However, the other half of the blame still falls on the website, since the owner should consider the impact of not supporting a widely-used browser.
SE used to do that, still supporting IE8 and IE11 until six years after their respective releases, but now they don't.