While adding a Gmail account, no popup shows, failed suddenly.

Preliminary: 1. I need to use proxy to visit `gmail.com` 2. The proxy setting in Thunderbird was tried with "Use system," "Auto-detect," and "Manual." but none of these worked. 3. The proxy setting in Firefox works well. (by visiting `gmail.com` and then `mail.google.com` redirected) Issue: As shown in the images, neither Account Creation page nor the new Account Hub is working. They found configurations of Gmail in Mozilla ISPDB, but when I pressed 'continue', no popup window appeared, and an failure suddenly occurred (just in several milliseconds): "Authentication error. Unable to log in at server. Probably wrong configuration, username or password."