IPvFoo is a Chrome/Firefox extension that adds an icon to indicate whether the current page was fetched using IPv4 or IPv6. When you click the icon, a pop-up appears, listing the IP address for each domain that served the page elements.
Everything is captured privately using the webRequest API, without creating any additional network traffic.
https://chrome.google.com/webstore/detail/ipvfoo/ecanpcehffngcegjmadlcijfolapggal
https://addons.mozilla.org/addon/ipvfoo/
https://microsoftedge.microsoft.com/addons/detail/ipvfoo/dphnkggpaicipkljebciobedeiaiofod
(You can also run the Chrome version on Edge, as they are identical.)
IPvFoo cannot be ported to Safari because the webRequest API does not report IP addresses. In theory, a Safari extension could do its own DNS lookups over HTTPS, but such behavior is beyond the scope of IPvFoo.