Hi Shubham, I hope your doing well despite the problem you are experiencing now and I'm sorry for that. For that let me try to assist you.
As for Firefox support on Windows Server, here is a link/reference of which Firefox support on Windows
https://en.wikipedia.org/wiki/Template:Firefox_...
Disclaimer: The link above is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the site before you decide to download and install it.
It is identified that Server 2012 and 2012 R2 is not anymore supported by 122, but only 2016 and later.
I hope this helps. Please let me know if I didn't address your problem. Don't hesitate to ask for further assistance.
Regards,
Arnel