Thunderbird support is located here: https://www.mozilla.org/en-US/thunderbird/

But let's try this out first;

Did you have problems with the prior Firefox/Thunderbird versions? Do you know if the programs or Windows had updates? Sometimes Windows updates don't work properly.

What's your computer system and Firefox version? +++++++++++++++++++++++++++++++++++++++++++++++++ Let’s do a full clean re-install;

Note: Firefox comes in three or more folders on all computers. They are;

Maintenance: (Programs Folder) <Windows Only> Firefox itself: (Programs Folder) And two folders in the profile of each user on the computer for each Firefox profile for that user.

If you remove the Firefox folder, the user profiles would not be affected.

Download Firefox For All languages And Systems {web link}

Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86) Note: Check Both Folders

Mac: Open the "Applications" folder. https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it. See Install Firefox on Linux; https://support.mozilla.org/en-US/kb/install-firefox-linux

If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory. http://www.mozilla.org/firefox#desktop ++++++++++++++++++++++++++++ Look for, and remove any Mozilla or Firefox program folders. Do not remove the Mozilla Thunderbird folder if there is one.

Do Not remove any profile folders.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. +++++++++++++++++++++++++++ If there is a problem, start your Computer in safe mode and try again.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode This shows how to Start all Computers in Safe Mode; Free Online Encyclopedia

https://www.youtube.com/watch?v=rFvkEhVdp14 Computer Freezing-Crashing After Windows 10 Update

Can not remove Firefox entirely. Eleven temp files (nsh730A, nsw7DEA etc) remain in the Firefox folder in Programs. Attempts to remove them are unsuccessful with the message "Can not remove files, open in Firefox" This occurs after a clean reboot. No programs or processes related to Firefox are shown in Task Master. Attempts to install from the above source (with temp files still present) are unsuccessful as progress stops at about the 75% range. Firefox will then open and the home page will appear but will be nonresponsive once the first keystroke is made. Running Windows 10 Home, version 10.0.17763 BIOS ID F.41 HP laptop17-Ca0xxx

Start your Computer in safe mode with network support. Now remove those folders. After, reboot.

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Thank you. I started in safe mode and removed the files. I downloaded and installed a new Firefox. It installed and opened. It operated properly for a few minutes and then changed to "Not Responding" As I stated at the beginning Mozilla Thunderbird also is "Not Responding." I am at a loss as to how to fix these issues. Unfortunately, I have not found a help page for Thunderbird like this one. Thanks again for your help.

Raylock1 said

I have not found a help page for Thunderbird

https://www.mozilla.org/en-US/thunderbird/

It operated properly for a few minutes and then . . .

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?