I think we're probably at a mature enough point in websites-as-documents that browser compatibility won't be an issue, except in very specific more cutting edge

I think we're probably at a mature enough point in websites-as-documents that browser compatibility won't be an issue, except in very specific more cutting edge media like 3d where they're dependent on non-standard features. However, on the apps side, there's definitely a preference for Chrome. I've noticed a couple web apps over the past few years do this, recently and most notably Coda (https://coda.io https://coda.io).