Hello Jasprit, a Firefox profile is a collection of bookmarks, browser settings, extensions, passwords, and history i.e. all of your personal settings. So all of these settings can be changed by creating custom profiles. By using default profile too, you can change user agent, default download directory, browser versions etc. The Profile Manager allows you to create, remove, rename, and switch profiles. For example, the following lines of code will set the preferred language to french:
FirefoxProfile profile = new FirefoxProfile();
profile.setPreference(“intl.accept_languages”,”fr”); //set the language to french
driver = new FirefoxDriver(profile);
driver.get("http://google.co.in");