When you start the process you enter your name email address and password. <img src=https://assets-prod.sumo.prod.webservices.mozgcp.net/media/uploads/images/2024-03-29-02-35-24-7ec668.png> However historically I think I recall xfinity is Comcast. I also think you might want to check that you have not locked Thunderbird out of your Comcast mail account by using this setting https://www.xfinity.com/support/articles/third-party-email-access Thunderbird has a database of settings and Comcast is included in that database. https://autoconfig.thunderbird.net/v1.1/comcast.net Unless there is an issue with your firewall allowing Thunderbird access to the internet it will always notify you that it has found settings for your account. When you click on the test button you actually try and use those settings for the first time. Failure always prompts a question about passwords, there was a time when they were the weak poinbt. Security software has overtaken that. The reality is it is far more common for antivirus products to block the connection attempt. Norton's used to have a SONAR feature that was basically guaranteed to mess up the new account wizard. But loads of other antivirus products mange to mess things up using self signed encryption certificates to scan mail. Try disabling your antivirus product while you configure the account and see if it goes any better.