The authentication problem encountered when creating a new Gmail account in Thunderbird can be solved as follows:
1. Set Thunderbird in safe mode
If Thunderbird is not running: Start Thunderbird in Safe Mode by holding down the option key while starting the application.
If Thunderbird is already running: At the top of the Thunderbird window, click the Help menu, select the Restart with Add-ons Disabled… menu item and then click the Restart button in the dialog box.
2. Find and open config editor in TB (equivalent of FF about:config)
To access the config editor, go to Thunderbird > Preferences, select the Advanced panel, select the General tab, and click CONFIG EDITOR
3. In Config Editor, find the entry:
and set the correspondent value(true) by double-clicking on it.
4. Restart your Thunderbird client program normally and try again to set the Gmail account.
5. Once again Gmail credential window and allowance confirmation from Google will be presented to you as security measure.
6. Everything will work fine from now on.