Try Safe Mode Thunderbird

Did not make any difference in startup time.

Are the two other PCs also launching the same (or copy of the same) profile?

My wife and I each have a laptop. I have a different profile than she does. Both of our profiles are in the profile folder on both machines but I run mine and she runs her profile. Hope that is helpful. I am far from a computer garu.

Restart Windows in safe mode with networking then launch Thunderbird normally.

Safe mode cut the load time about in half! Shouldn't there be an hourglass or spinning wheel when Tbird is loading? Instead there is no indication at all. Thanks for your efforts.

You can reboot back to Windows 10 normal mode. Your antivirus or other security program is most likely the reason for the poor performance you're experiencing in Windows normal mode. They are notorious for interfering with startup and normal running of other programs, so you need to whitelist Thunderbird's profile folder from your antivirus' shields to make sure Thunderbird's filesystem activities are not interefered with. See the following articles:

https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues Profiles - Where Thunderbird stores your messages and other user data

Only antivirus I have is windows defender. I excluded the profiles folder and it made no difference. Rather than take a lot of time troubleshooting the problem I am just going to live with slow startup. I appreciate your suggestions, I thought there would be an easy fix since it showed up with the new release and the older versions worked fine.

There is no easy fix because this is unique to your setup. V78 starts up just fine on my systems. As soon as the icon is clicked, the system responds immediately as indicated by the "busy" mouse pointer and in a few seconds, Tbird shows up. It's slightly slower than V68 startup, but not as slow as you describe. From your description, it seems there is a delay between clicking the icon and your system executing the launch, and no indication of the execution taking place. Subsequent launches on my systems take place almost instantly, for example when I quit Tbird and relaunch it. The first startup after a system reboot is slightly slower.

The only other thing I can think of that you can try is a clean installation of Tbird. This means you remove Thunderbird's program files and then reinstall Thunderbird as follows :

1. Download the latest version of Thunderbird from thunderbird.net and save the setup file to your computer.
2. After the download is complete, close all Thunderbird windows (Click Exit/Quit from the menu button on the right).
3. Delete the Thunderbird installation folder, which is located in one of these locations, by default:
   • Windows:
     • C:\Program Files\Mozilla Thunderbird\
     • C:\Program Files (x86)\Mozilla Thunderbird\

1. 1. Double-click the downloaded installation file and go through the steps of the installation wizard.
   2. Once the wizard is finished, choose to open Thunderbird after clicking the Finish button.

WARNING: Do not use a third party remover/uninstaller as part of this process, because that could permanently delete your Thunderbird data, including but not limited to, extensions, emails, personal settings and saved passwords. These cannot be recovered unless they have been backed up to an external device!

I will give this a try and let you know if it helps. May be a few days.

Sorry I took so lon to try your suggestion. Reinstalled Thunderbird did not help. I added a new profile and it loads quickly like ver 68 used to do. I have lots of emails in a number of folders so it must be the way ver 78 loads the database. It did not slow ver 68 with my regular profiles. Guess I will live with it even if it is irritating. Thanks for trying.

Version 78 has not fundamentally changed how folders are loaded.

Do you have any calendars?

I do use Lightning and Google calendars. I disable Google calendar and still had the problem. I went back to Ver 68-12 and all is well again. I did lose part of an address book when downgrading but all in all it was worth the time. Thanks for the inquery.

How many accounts?

If you should revisit version 78, you can get a performance profile and post the URL of your findings. https://support.mozilla.org/en-US/kb/profiling-thunderbird-performance