On 2023-04-17 17:52, Carlos E. R. wrote:

Your browser has real working IPv6 address - but is avoiding using it. We're concerned about this. [more info]

→ https://test-ipv6.com/index.html.en_US#found

I don't understand this. Meaning, what can I do to make firefox use IPv6 
and why exactly it doesn't?

You can configure your computer to prefer IPv4 or IPv6

How to type ipv6-address and port number in URL bar?

That can be tricky. Best to use host names.

Any reason you're using DHCPv6 instead of SLAAC for the LAN? Thanks to some genius at Google, Android doesn't support DHCPv6.

Ok, I can find my own router address doing a traceroute6 to google or any 
outside address. The first line. Huh, will that be the external or the 
internal address of it?

Routers often use link local addresses.