If you'd like to run multiple Firefox instances on Windows without having to fiddle with the profile settings and maybe run different versions too, you can always install both Firefox and Firefox portable (no need to have the same version).
Simply browse to the Firefox portable installation directory and edit the FirefoxPortable.ini file changing AllowMultipleInstances=false to AllowMultipleInstances=true
That's it, you can now run the two browsers side by side.
