gMail would not accept my password and research revealed the following explanation at
https://support.google.com/accounts/answer/6010255:
"Google may block sign in attempts from some apps or devices that do not use modern security standards. Since these apps and devices are easier to break into, blocking them helps keep your account safer.
"Some examples of apps that do not support the latest security standards include:
The Mail app on your iPhone or iPad with iOS 6 or below
The Mail app on your Windows phone preceding the 8.1 release
Some Desktop mail clients like Microsoft Outlook and Mozilla Thunderbird."
By turning on the "Access for less secure apps" at
https://www.google.com/settings/security/lesssecureapps the problem was solved, but apparently it is less secure because Thunderbird does not support the latest security standards.
Is Mozilla doing anything to correct this security problem?