can install Google accounts as POP but not IMAP accounts

I can install two google accounts as POP accounts but not as IMAP accounts. When I try to install them as IMAP accounts: 1. In Thunderbird, I enter my log-in credentials in the Mail Account Setup window and press "Continue." A message appears in the window that says "Configuration found in Mozilla ISP database." I press "Done." "Checking password" appears and the circle goes around and around. A message in the window says "Username or password invalid." 2. At the same time, a window opens that says "Google Sign in to continue to Mozilla Thunderbird Email." It shows my email address. When I press "Next" in that window, nothing happens. 3. If I close the Google sign-in window, a message in the Thunderbird window then says "Configuration could not be verified--is the username or password wrong?" As I said, I can install the POP accounts successfully using the same login credentials. Any suggestions would be appreciated.