Hello! I've had this problem 1 year ago and I solved it activating 2-step verification for all my Gmail accounts, but now it's back! Basically, Thunderbirs can't connect to all my Gmail accounts and keeps asking me to do the web login,but: 1) It doesn't happen with all of them at the same time. I have 5 Gmail accounts. Sometimes 3 don't work, sometimes two, sometimes just one. 2) When I login on webmail, the problem goes away but after a few hours comes back. Not always with the same Gmail accounts. As I said, it was about a year I did not have this problem anymore and now it's back. May be a coincidence, but this happened after I installed Windows 10 October update. Thank you for your help!