Firefox installations as normal user
I have FF ESR installed and when new update comes I have 2 installations (if uninstalled whole FF ESR previously) under Windows Apps & Features (original installation (which can be versions ago) and latest version) on non-admin account (only 1 on admin account).
While it's not big issue (disk space wise or other wise) would be nice that had only 1 FF ESR not 2 under Apps & Features as normal user since it gets bit tiresome to uninstall and re-install Firefox every couple months to get rid of earlier update's leftovers.
Opaite Mbohovái (4)
Sometimes the Firefox installer doesn't remove the old Firefox version from the Windows Registry, but merely adds the new version under installed programs. You can check the install location of both versions and possibly use a registry cleaner to remove the older version if both point to the same folder. It is also possible that you have a 32-bit and a 64-bit version installed.
Well cleaning registry probably helps only until next ESR version comes. There are quite a many registry entries about 115.6 (1st installation ~month ago) and .6 and .7 point to same folder etc.
Don't have 32bit version installed.
What security software do you have in case that is interfering?
Well Comodo Internet Security is main but it doesn't block any Mozilla's installations (FF or SM).