Okay so first of all, in the code you've used above, your not creating a new Firefox Profile. Your just creating a new object instance of Firefox profile class. And moreover your not creating a profile for firefox using Selenium, but instead your creating a Firefox profile for your WebDriver from the already existing profiles in Firefox.
FirefoxProfile ffprofile = new FirefoxProfile(new File("D:\\Selenium"));
WebDriver driver = new FirefoxDriver(ffprofile);
When you execute this command, a new object of Firefox profile will be instantiated and the profile setting which will get imported will be those settings saved in the file in the mentioned location: "D:\\Selenium".
At this point, do note that you are using an existing profile and not creating a new profile. Selenium cannot do it for you.
If you want to create a new profile, then follow this documentation: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles