When listening on localhost on an unprivileged TCP port any other process could open the port first and provide a similar UI. Opening the port may even trigger

When listening on localhost on an unprivileged TCP port any other process could open the port first and provide a similar UI. Opening the port may even trigger the original process to chose another free port and the malicious software could take the requests from the users browser on the usual port and forward them to the new port. UNIX sockets would of course solve this issue.