Everytime I try to access any Tor website with .onion,his message appears

Unable to connect Firefox can't establish a connection to the server at aaaaaaaaaa.onion.

The site could be temporarily unavailable or too busy. Try again in a few moments. If you are unable to load any pages, check your computer's network connection. If your computer or network is protected by a firewall or proxy, make sure that Tor Browser is permitted to access the Web.

I'm using Tor as browser. And when I go to this: https://check.torproject.org/

It says it is configured to use Tor