I've logged into the browser numerous times, check and re-checked the password. On another account, on the same pc, Thunderbird connects to this Gmail account fine. So, it's certainly not a question of configuring the account to allow Thunderbird access.
Again, on the same pc, a different account accesses this Gmail account through Thunderbird without any problems.
Why does Thunderbird keep insisting that there's a password problem? I'm just not that bad at typing in passwords...
Unable to login at server. Probably wrong configuration, username or password.