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

I believe I have done a clean reinstall as described but the problem persists. After the reinstall, FF opens and I can close the browser and reopen no problem. The next day, however, I get the same error and FF won't open until I redo the reinstall process.

Richard1111 said

The next day, however,

Sounds like something is corrupting the files.

Do a clean install again. Open the Firefox folder and check the date of the files. When the program fails again, check the file date again.

You may have ad/mal-ware. Further information can be found in this article; https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware?cache=no

Run most or all of the listed malware scanners. Each works differently. If one program misses something, another may pick it up.

Thought your help had solved the problem. Able to use FF 2 days in a row, but today got the couldn't load xpcom. Ran malwarebytes, clean; ran adwcleaner got 77 PUPs and PUAs; ran microsoft scanner software got 1 file. I have been reinstalling using a file downloaded from FF site "Firefox setup 74.0.exe" Is this the correct reinstall? I downloaded it from https://www.mozilla.org/en-US/firefox/all. Thanks for your help. I really thought after finding the suspicious files and quarantining I was okay, but something is still going on.

Richard

I called for more help.