First, I have no expertise in the problem with restarting. But, on the 700 correspondents, you can save those by copying two files: abook.sqlite and history.sqlite to a safe place. Then, if you eventually need to do a full uninstall and reinstall, these two files can be copied back into the profile. You can locate the profile in Windows by entering %appdata% in the search box on the task bar and then click the thunderbird folder and then the profiles folder and then your profile.

Thank you David for trying. Do the two files to be copied are spelled with a G or a Q?

Yet my problem isn't solved. Can someone else help me to get Thunderbird back on my screen without the non-stopping note to restart, even though I do it endless times?

the letter is Q. you might try booting windows to safe mode and then uninstall thunderbird while retaining profile. then reboot and install fresh.

> restart to complete the recent updates.

Delete the program directory c:\program files (x86)\Mozilla Thunderbird\ (confirm that is the current location by visiting Help > Troubleshooting information) nd reinstall from https://www.thunderbird.net/thunderbird/all/