If a server has only IPv6 address without domain name, how can I connect to server from my web-browser?
According to RFC2732, literal IPv6 addresses should be put inside square brackets in URLs, e.g. like this:
Of course, you have to have end-to-end IPv6 connectivity to that host. E.g. if the server is not inside your own local network, you need to have IPv6 connectivity, either via your ISP (rare), or via some kind of IPv6 in IPv4 encapsulation (tunnel).
Put the ipv6 address into your browser address bar like you would a dns name or an IPv4 address, except enclosed in square brackets:
(example with localhost)
This is supported in Chrome, Firefox, IE and probably other browsers.
Note that you need to have IPv6 working on your OS, and every device in the path to the destination (including proxy servers if you use one).