To specify and browse a website using an IPv6 address with Firefox or Opera, you will need to enter the IPv6 address in the address bar of the web browser.
Here are the steps to specify and browse a website using an IPv6 address with Firefox or Opera:
Open Firefox or Opera and go to the address bar.
Type the IPv6 address of the website you want to visit, preceded by "http://" or "https://". For example:
http://[2001:0db8:85a3:0000:0000:8a2e:0370:7334]/Source:.wwwlautturi.com
This is the IPv6 address of the website, enclosed in square brackets.
With these steps, you should be able to visit the website using its IPv6 address.
Note: Some websites may not support IPv6, in which case you may need to use the website's domain name or IPv4 address to access it. You can use the "ping6" command to check if a website is reachable using IPv6.