Do you recall whether Firefox was preinstalled on your distro, or you installed from a Zorin repository, or you installed from Mozilla's website?

If your Firefox isn't updating itself, you could download the latest installer from whichever one you used before. If the installer won't run, check the system requirements to see whether perhaps a different library is needed (as a Windows person, that's about as much as I can really tell you about that part):

https://www.mozilla.org/firefox/115.0/system-requirements/

If you are using the tarball version from https://www.mozilla.org/firefox/all/#product-desktop-release then make sure the Firefox folder has read/write permissions for the user account so Firefox can do internal software updates from Mozilla.

Not sure what the most current version of Firefox packages are for the older Ubuntu 20.04 which is what current Zorin OS is based on.

https://linuxconfig.org/how-to-install-uninstall-and-update-firefox-on-ubuntu-20-04-focal-fossa-linux