Is it a corporate computer?

No, It's my personal computer that I don't use for work

Policy can be implemented by a "policies.json" file in your Firefox installation or Group Policy Objects (GPO). You can delete them and monitor what software re-creates them with Process Monitor and auditing.

Weird, whenever I go to "C:\Program Files\Mozilla Firefox\distribution\policies.json" and open the file, all I see is this line of code which doesn't include either of the policies listed above

policies.json code below: " {

 "policies": {
   "Certificates": {
     "ImportEnterpriseRoots": true
   }
 }

} "

You can inspect the Mozilla and Firefox keys with the Windows Registry Editor in HKEY_LOCAL_MACHINE and in HKEY_CURRENT_USER with the Windows Registry Editor to see whether GPO policy rules are active.

• HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Mozilla\Firefox\
• HKEY_CURRENT_USER\SOFTWARE\Policies\Mozilla\Firefox\

The mere presence of the "Mozilla\Firefox\" key is sufficient to make Firefox display this notification, so if you have the Firefox key then remove it and only leave the Mozilla key or remove this key as well if it is empty.

• HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Mozilla\Firefox\ =>
  HKEY_LOCAL_MACHINE\SOFTWARE\Policies\

More info:

• https://support.mozilla.org/en-US/kb/customizing-firefox-using-group-policy