[evgpbfhnr]

And it gets even more fun when browsers such as firefox implemented this, then decided no we won't do it and removed the feature -- now there's no way to access your router web interface over link-local address...

(rationale being that whatwg said no: https://github.com/whatwg/url/issues/392 ; firefox bug https://bugzilla.mozilla.org/show_bug.cgi?id=700999 )

The "solution" is to use a proxy such as https://github.com/twisteroidambassador/prettysocks/tree/ipv... which incidentally encode the % as a `s` and handle special URLs like this http://fe80--1ff-fe23-4567-890as3.ipv6-literal.net for you through the socks dns resolution feature... I've never found anything else that works recently -_-

[Dagger2]

I very much didn't test it, but this patch might do the job on Firefox (provided there's no code in the UI doing extra validation on top):

  --- a/netwerk/base/nsURLHelper.cpp
  +++ b/netwerk/base/nsURLHelper.cpp
  @@ -928,3 +928,3 @@ bool net_IsValidIPv4Addr(const nsACString& aAddr) {
   bool net_IsValidIPv6Addr(const nsACString& aAddr) {
  -  return mozilla::net::rust_net_is_valid_ipv6_addr(&aAddr);
  +  return true;
   }

Or if you actually wanted to do some validation, pass the address to getaddrinfo():

  bool net_IsValidIPv6Addr(const nsACString& aAddr) {
    struct addrinfo *res, hints = {.ai_flags = AI_NUMERICHOST};
    int err = getaddrinfo(aAddr.get(), nullptr, &hints, &res);
    if (err) return false;

    bool isValid = res[0].ai_family != AF_INET;

    freeaddrinfo(res);
    return isValid;
  }

This way it's valid if your OS considers it a valid address.

[zamadatix]

Could you do the same trick just putting a temporary entry in the hosts file?