On Windows, there’s no need to manually change the Registry in order to run multiple versions of Firefox. The 17 different versions of Firefox which are installed in this machine work just fine, with multiple versions executing at the same time without having manually modified the registry. This includes Release, 52 ESR, Beta, Developer Edition, Nightly, and various other older versions used for testing at different points (many of all of the above have both 64 bit and 32 bit versions). Any/all of which run concurrently. [Yeah, 17 different versions is a bit excessive. Many of them are specific versions which were installed for add-on compatibility testing.]
It does make it more convenient if you create a shortcut for the version which either runs a specific profile, or has the Profile Manager appear first to allow you to select the profile to use, or create a new one. You can do that by adding the command line options (just add them to the shortcut’s “Target”): -no-remote -ProfileManager