Yeah, probably easiest & best to uninstall and reinstall with a package manager. Anything that manages updates will likely have Firefox configured to not check for updates

If you are a GUI kind of guy try your OS’s app store.

Otherwise apt, yum, homebrew or winget should do the trick :)

Heres an informative forum post about it: https://superuser.com/questions/1370165/disable-or-control-upgrading-of-firefox