Hello, Have you read this discussion here: https://support.mozilla.org/en-US/questions/1389130 There are some good options you could try.

What happens if you use imap.comcast.net, 993, SSL/TLS, OAuth2 authentication, email address; smtp.comcast.net, 587, STARTTLS, OAuth2 authentication, email address? TB supports OAuth2 on Comcast since v.115.6.1.

Also, make sure 3rd-party access is enabled:

https://www.xfinity.com/support/articles/third-party-email-access

This did not work. Third party is checked. I tried the two settings at the top of your email. My current setting is: Smtp.comcast.net, 465,SSL/TLS, Normal Password. I shut down and restarted my computer before testing each setting. Your suggested settings did not work. Comcast email is still working. I have remember my device turned on in login to Xfinity.