After the last update, all the messages sent to my comcast account are also downloading to my gmail account.
After the last Thunderbird update, all the messages downloading to my comcast account are also downloading to my gmail account. Then, as I go through the mails in the comcast account and delete them, they are also deleted from the gmail account, after a while.
I actually have two gmail accounts, but the messages to comcast are also downloading only to one of them, which is my main Google login. The other gmail account is just extra.
ప్రత్యుత్తరాలన్నీ (1)
sounds to me like you have either set up forwarding in the comcast web site to gmail or have set up gmail to collect your mail from comcast. I do not think this has anything to do with Thunderbird at all.