I've seen plenty of websites with a "Works best in Chrome" banner, usually because they use some non-standard web API. Though, I've seen plenty that clearly just didn't care to test outside of Chrome, so they just assume you're using that.
My gripe about "Safari being the new IE" was more about how broken some websites can be in Safari and having no good way of knowing or testing that. At work, my boss said out website didn't look quite right on his iPhone and it took more work than I'd thought to track down the piece of CSS that Safari rendered differently for some reason.
Personally, I don't use macOS or iOS and I also use Firefox. Generally, things seem to work the same between Firefox Chrome and Safari, with Safari needing the most amount of "tweaks".
My gripe about "Safari being the new IE" was more about how broken some websites can be in Safari and having no good way of knowing or testing that. At work, my boss said out website didn't look quite right on his iPhone and it took more work than I'd thought to track down the piece of CSS that Safari rendered differently for some reason.
Personally, I don't use macOS or iOS and I also use Firefox. Generally, things seem to work the same between Firefox Chrome and Safari, with Safari needing the most amount of "tweaks".