How to Upgrade Firefox from 32-bit to 64-bit in Windows Without Reinstalling
 

Most web browsers are installed in Windows as 64-bit versions by default, Firefox being the exception. If you installed the default download of Firefox, you have the 32-bit version, not the 64-bit version, even if you’re running a 64-bit version of Windows.

https://www.howtogeek.com/298291/how...-reinstalling/