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 free to use malware scanners. Each works differently. If one program misses something, another may pick it up.

After the above; 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}

Firefox ESR; Extended Support Release {web link}

Beta, Developer, Nightly versions https://www.mozilla.org/en-US/firefox/channel/desktop/

Install Older Version Of Firefox {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.

How to Start all Computers in Safe Mode; {web link} Free Online Encyclopedia

I am unable to check for anything in the first step as Firefox is not available to open. I did scan for malware with Panda and Malwarebytes, and found nothing. I deleted all Mozilla folders from both program files, rebooted, ran a reg cleaner, and when I tried to reinstall, there was an error included in a screenshot here. I booted in to safe mode and tried to install, and the installer went away after the extraction screen finished and not install occurred.

You can check for issues caused by a corrupted or incomplete Visual C++ installation that is missing runtime components (Redistributable Packages) required by Firefox, especially VCRUNTIME140_1.dll.

In that case, I would install both 32-bit and 64-bit "Visual Studio 2015, 2017 and 2019" downloads, (x86: vc_redist.x86.exe and x64: vc_redist.x64.exe) from https://support.microsoft.com/help/2977003/the-latest-supported-visual-c-downloads

Uninstalled and reinstalled and see the same issue trying to reinstall Firefox. I found the following in an install log in C:\Program Files\Mozilla Firefox folder. We also had a user report that Thunderbird was deleted early this morning, and these two files were found to be in error on his laptop as well.

DLL Registration

 ** ERROR Registering: C:\Program Files\Mozilla Firefox\AccessibleMarshal.dll **
 ** ERROR Registering: C:\Program Files\Mozilla Firefox\AccessibleHandler.dll **
 Recorded: C:\Program Files\Mozilla Firefox\mozwer.dll

In a case where we were able to fix a Firefox installation, we had to copy the C:\Program Files\Mozilla Firefox folder from a working PC to get things back up and working, but when the PC is rebooted, everything disappears again.

I called for more help.

Fred, we have found the problem here. It has something to do with lack of security rights for the user. Just figured that out late yesterday evening.

That was very good work. Well Done. Please flag your last post as Solved Problem as this can help others with similar problems.