You forgot {}
Do it in this way:
if(browser.equals("Mozilla"))
driver = new FirefoxDriver();
else if(browser.equals("Chrome")){
System.setProperty("webdriver.chrome.driver", "F:\\chromedriver_win32\\chromedriver.exe");
driver = new ChromeDriver();
}else if(browser.equals("IE")){
System.setProperty("webdriver.IE.driver", "C:\\Users\\Ryuk~\\Downloads\\IEDriverServer_x64_2.43.0\\IEDriverServer.exe");
driver = new InternetExplorerDriver();
}
driver.get("https://gmail.com");
System.out.println(driver.getTitle());
use if without {}
is only possible if you have only one line, like your first part