Using v128.2.0esr (64-bit) on Windows 10 Trying to add GMail, had no problem adding other email accounts. I follow the same process- enter creds and click save/continue. Thunderbird opens a new window for me to sign into GMail to complete the process. It results in a 404 error: 400. That’s an error. The server cannot process the request because it is malformed. It should not be retried. That’s all we know. Screenshots attached