This is the place to work on the custom error messages that we want to have in Tor Browser instead of Unable to connect and The proxy server is refusing connections. The rationale for this can be found in tails#9473.

For the record, these are the default error messages:

The proxy server is refusing connections

Firefox is configured to use a proxy server that is refusing connections.

• Check the proxy settings to make sure that they are correct.
• Contact your network administrator to make sure the proxy server is working.
• Check your internet connection

Unable to connect

Firefox can't establish a connection to the server at www.google.com.

• 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.