Password sent by Thundebird is rejected by Comcast

I setup a new email address with Comcast. I can send emails, but can not receive them. When I open T-Bird I get the following message: "Alert-sending of password for user xxx@comcast.net did not succeed. Mail server mail.comcast.net responded: LessSecureAuthDisabled" This leads to a cycle of entering a new password & so on. The password works on xfinity.com & is shown in my T-Bird settings. Comcast says my settings are all correct & it is a T-Bird problem. I have had another Comcast email address with T-Bird as my email client for many years & it still works fine. It uses the same mail.comcast.net server as the new address. I have had a webhost a/c with 2 addresses & T-Bird for years that also work fine. I have installed the new email address on my Windows 8.1 with a very old version of T-Bird & on my Windows 10 with the latest version of T-Bird. I still can't receive any emails. If I send an email from any 3 of the 4 accounts to the other 3 accounts, the old mail.comcast.net server address receives all 3 & the new address, which also uses mail.comcast.net, receives none. The 2 accounts on the webhost receive some of the 3, but not all 3. Any help would be greatly appreciated.