browser feature detection is the way grown up developers have been doing this for several years now. user agent sniffing is dumb because it bundles a ton of assumptions with a high upkeep requirement, all wrapped up in an unreadable regex. It's been bad practice for ages; I'd be surprised if that's how Amazon is doing it still.
the realistic answer to this line of questioning is : "we don't care about the edges because they constitute such a small percentage of the user base."
