This is fixed in TB 68.2.1 for gmail IMAP accounts, but for earlier versions, apply the workaround mentioned here:

https://bugzilla.mozilla.org/show_bug.cgi?id=1592407#c22

Tools/Options(Mac:Preferences; Linux:Edit/Preferences)/Advanced/General/Config. editor, double-click general.useragent.compatMode.firefox to true.

This should also fix google calendar and contact sync. in 68.2.1 until updated Provider and gcontactsync add-ons are released.

Thanks very much. Is this change made in Thunderbird or Firefox?

I know how to access the value in Firefox (about:config) however, I have no idea how to do it in Thunderbird.

Thanks

Make the change in TB. Press Alt if the Menu Bar with Tools is hidden on Windows. On Linux, if you can't see Edit/Preferences, click the 3-bar AppMenu icon, Options/Options.

sfhowes...thanks very much. That did it as I am now receiving GMail in TBird. DrP

I have TB 68.4.2 and Windows 10. Since 01.22.20 I cannot connect to the gmail server. The server says it is blocking TB because it is a 'less secure app'. But TB reports that it cannot find the gmail server settings. I have set it up manually, offline ... tried everything but no luck. I have 3 gmail accounts. One has no problem, one doesn't download all my email into TB and the third one stopped working on 01.22.

I have removed the account, turned off Norton AV and Malwarebytes, set up the account manually - nothing. Cannot download my messages.

Is there any hope or solution other than reading them online in my mail account?

Start your computer in Windows safe mode with networking to eliminate interference from any startup security apps. Open TB and Tools/Options/Security/Passwords/Saved Passwords, delete all passwords, restart TB. In the Server Settings for each gmail account, set the authentication to OAuth2. If you have gmail POP accounts, update to 68.5 which supports OAuth2 for gmail POP. Set the authentication for all gmail smtp servers to OAuth2. Check that cookies are allowed in Options/Privacy. When you connect to an account, enter the regular account password in the OAuth browser window (not an 'app password').

http://kb.mozillazine.org/Using_Gmail_with_Thunderbird_and_Mozilla_Suite

If this works in Windows safe mode, either remove Norton AV or add the TB profile folder as an exception or exclusion in NAV, and disable scanning of secure (SSL) connections.

Hallelujah - success! A million thanks, this problem has caused so many lost hours and frustration, now fixed thanks to you.

As above, but I did it this way and it worked. Thunderbird had my old password saved, you need to delete that and retrieve mail to login to gmail again and save that password. It worked instantly.

OPEN THUNDERBIRD

IN THE MENU BAR GO TO Tools/Options/Security/Passwords/Saved Passwords

SEARCH FOR THE GMAIL ACCOUNT YOU ARE HAVING TROUBLE WITH AND CLICK 'Show Passords' and 'yes'.

FIND THE GMAIL IMAP OR POP ACCOUNT AND IT'S SMTP COUNTERPART AND 'Delete' JUST THOSE (I HAVE SEVERAL GMAIL ACCOUNTS AND SOME HAVE THE CURRENT PASSWORDS AND ARE FINE).

CLOSE THE TOOLS AND CLICK THE DOWN ARROW TO 'GET MESSAGES' JUST FOR THE ACCOUNT YOU HAVE AN ISSUE WITH.

THUNDERBIRD WILL OPEN A BROWSER WINDOW FOR GMAIL THAT ASKS FOR YOUR LOGIN AND PASSWORD, ENTER THE CURRENT INFO.

IT WILL PROMPT FOR YOUR PERMISSION, SO ACCEPT.

I did this and instantly got my gmail back in Thunderbird. You need to do the same steps for SENDING email with the SMTP account, so after you do the above, click to WRITE and email. Be sure the account you had a problem with is in the 'FROM' line (if you have multiple gmail accounts you can use the drop down to select it). DRAFT your email and send. You will get the same BROWSER LOGIN as with your IMAP/POP EMAIL.

It worked for me!