What isn't working exactly? It sounds like you are able to launch Firefox at least.

Try reinstalling the Visual C++ Redistributable.

Temporarily disable any third-party antivirus or security software, this may require rebooting into Windows Safe Mode with networking enabled.

Thanks for the help. I want to better describe what is happening and what we have tried.

• A few weeks ago FF stopped working on 2 PCs. When we clicked the icon it flashed open & then closed in less than a second.
• We repaired & reinstalled on both PCs. Nothing changed.
• We created new profiles on both PCs. Nothing changed.
• When we open FF in Troubleshoot mode, it will stay open longer but still shuts in 30 seconds to a minute.
• We removed & reinstalled what we think are the correct C++ installation packages. Nothing changed.
• We took your recommendation to temporarily disable our AV software (McAfee). The problem is still there.

At this point when we click FF it will stay open for a brief time - usually less than a minute.

One thing that I noticed about C++ was than when viewed in Add/remove programs, there were 5 installed items listed. three of them had been updated or installed in mid November, which is about when this problem started. As of right now the only one I have listed there is "Microsoft Visual C++ 2015-2022 Redistributable (x64) - 14.38.33130".

Thanks again

Try renaming firefox.exe to something else.

Do a full system scan for malware with a different AV brand like Malwarebytes.