IMAP Settings Not Working

I use "Betterbird" which is a clone of "Thunderbird" on my Linux workstation.  I have tried to set up my comcast IMAP account many times but it always fails.  I can set up the POP account OK.  My IMAP settings work on the web version of Xfinity eMail.  I have attempted to use every possible setting listed on the various help pages for connecting the IMAP account but it always fails with a "cannot connect" separate message window.  I am wondering if there is a glitch somewhere.  I have switched back to "Thunderbird" an attempted the same procedure and settings, but still receive the failure message.   I am out of ideas.  I would appreciate some advice.  Meanwhile I continue to use the Xfinity eMail web site.  BTW:  My IMAP settings work on both my Android phone and on my iPad devices -- all settings are the same as those put forth on the eMail connection settings pages.

Regards to the Group,

[Edited: "Personal Information"]