What bit version is your O/S?

whose said

C:\Program files\mozilla Firefox\firefox.exe headlines then the message show: C:\Program Files\Mozilla Firefox\firefox.exe is not valid Win32 application. How do I correct this problem?

Try downloading from www.mozilla.org/firefox/all/ and reinstalling.

Firefox 62.0 does require Windows 7, 8, 10 to run.

I'm still using Windows xp

Hmm well then your only option is to use the now End Of Life Firefox 52.9.0 ESR (32-bit).

http://archive.mozilla.org/pub/firefox/releases/52.9.0esr/win32/ English US http://archive.mozilla.org/pub/firefox/releases/52.9.0esr/win32/en-US/

Otherwise you need Windows 7 or later or consider dual booting with a light 32-bit Linux distro like Lubuntu or Xubuntu or some other light Linux options. Not as many still support the ancient 32-bit CPU's now days though as most support the 64-bit CPU's from AMD and Intel.

https://support.mozilla.org/en-US/kb/end-support-windows-xp-and-vista