System tor users won't be notified if the connection to the control port fails
In #42129 (closed) we removed the "restart Tor" prompt when the browser doesn't start the Tor process.
In !812 (merged) we're adding a warning to use check.tpo in that case, which is independent from the control port connection.
A case remains uncovered: a user set the address of their system tor correctly, but they haven't set the proper settings for the control port.
An idea is adding another blocking prompt, just like the restart Tor one, but with another message (basically: "We couldn't connect to the control port. Please check your settings. Your proxy settings might be still valid, but you won't have the circuit display") and just the "OK" button (we can't do anything in that case).
However, some users might get annoyed by this, but I don't like the idea of adding a checkbox to ignore this error.
Another idea could be a non-blocking notification, like the one for the language.