Sorry to hear about this problem. Can you look up your Windows 10 version this way:

In the Windows 10 system search box (usually on the Taskbar), type or paste winver and Windows should show that as a program on the Start menu. Click that and look for the Version line, which may vary. Mine shows

Version 1909

Do you have the newer version?

Please see the attachment

Thanks, it says you have version 2004, which is the most recent major update of Windows 10.

I think Firefox may include a copy of MSVCP140.dll in its own program folder:

C:\Program Files\Mozilla Firefox\

Is that missing, or is yours a later version (I've attached a screenshot of the right-click Properties dialog, Details tab, showing mine is from the 2017 version of Visual Studio)?

I do not see it

Hmm, that could explain why Firefox is trying to use the one in the C:\Windows\system32 folder. But I'm not sure where you can get a compatible copy of the file from a trusted source. Hopefully another support volunteer will have a good lead on that.