For future reference, there are various ways to work around lack of support for *.localhost in your OS:
(A) update local DNS resolver to something that supports subdomains
(B) set Gateway port provided by go-ipfs as HTTP proxy for fetching  *.localhost (this way no DNS lookup is done, gateway will take care of translating Host header into proper content path – fysa  ipfs-companion does this automatically in Firefox, until localhost is fixed upstream, so users do not need to do anything)
(C) use client which does not resolve localhost names, but hardcodes them to loopback device (right now its all Chromium-based browsers, but Firefox will soon follow, as noted in https://github.com/ipfs/in-web-browsers/issues/109#issuecomment-717248720