[isodude]

It depends on how you register things.

* Given that you can easily start up your own CA in a test bed, just use different domain names.

* Or use IP addresses directly, given that IPv6 i pretty abundant it's easy to just listen on many addresses at the same time. A nice thing is to just put the port number is the last octets: fd01::9000, fd01::0003:5565. If it's HTTPS you always use port 443, if it's another protocol, use another port. With iptables/nft you can translate all port 443 traffic towards a /96 to a single IP.

* Firefox does not seem to understand unix domain sockets, https://news.ycombinator.com/item?id=27941552. I'm assuming that you have a gateway in front that handles that aspect.

* Proxies in Firefox seems to understand that though, which means you can have a proxy that translate to unix sockets locally. That means you can basically run it to a namespaced application, using only http://<service>.localhost.