I'm using FirefoxOptions class to set the binary location with Firefox 52.0, GeckoDriver v0.15.0 and Selenium 3.3.1 as mentioned in this article - http://www.automationtestinghub.com/selenium-3-0-launch-firefox-with-geckodriver/
The java code that I used -
FirefoxOptions options = new FirefoxOptions();
options.setBinary("C:\\Program Files (x86)\\Mozilla Firefox\\firefox.exe"); //location of FF exe
FirefoxDriver driver = new FirefoxDriver(options);
driver.get("http://www.google.com");