How to download files in Mozilla using Selenium Webdriver

FirefoxProfile firefoxProfile = new FirefoxProfile();

firefoxProfile.setPreference("browser.download.folderList",2);
firefoxProfile.setPreference("browser.download.manager.showWhenStarting",false);
firefoxProfile.setPreference("browser.download.dir","c:\\downloads");
firefoxProfile.setPreference("browser.helperApps.neverAsk.saveToDisk","text/csv");

Here text/csv is a mime type, change this mime type depending on the file type you want to download

Popular mine types

PDF => application/pdf
Text file => text/plain
.exe => application/octet-stream
MS Doc => application/msword
xls => application/excel
.zip => application/x-compressed
.tgz => application/gnutar

How to download files in IE using Selenium Webdriver

public void clickAndSaveFileIE(WebElement element) throws AWTException, InterruptedException {

    Robot robot = new Robot();

    // Get the focus on the element..don't use click since it stalls the driver        
    element.sendKeys("");

    //simulate pressing enter          
    robot.keyPress(KeyEvent.VK_ENTER);
    robot.keyRelease(KeyEvent.VK_ENTER);

    // Wait for the download manager to open          
    Thread.sleep(2000);

    // Switch to download manager tray via Alt+N
    robot.keyPress(KeyEvent.VK_ALT);
    robot.keyPress(KeyEvent.VK_N);
    robot.keyRelease(KeyEvent.VK_N);
    robot.keyRelease(KeyEvent.VK_ALT);

    // Press S key to save          
    robot.keyPress(KeyEvent.VK_S);
    robot.keyRelease(KeyEvent.VK_S);
    Thread.sleep(2000);

    // Switch back to download manager tray via Alt+N
    robot.keyPress(KeyEvent.VK_ALT);
    robot.keyPress(KeyEvent.VK_N);
    robot.keyRelease(KeyEvent.VK_N);
    robot.keyRelease(KeyEvent.VK_ALT);

    // Tab to X exit key
    robot.keyPress(KeyEvent.VK_TAB);
    robot.keyRelease(KeyEvent.VK_TAB);

    robot.keyPress(KeyEvent.VK_TAB);
    robot.keyRelease(KeyEvent.VK_TAB);

    robot.keyPress(KeyEvent.VK_TAB);
    robot.keyRelease(KeyEvent.VK_TAB);

    // Press Enter to close the Download Manager
    robot.keyPress(KeyEvent.VK_ENTER);
    robot.keyRelease(KeyEvent.VK_ENTER);

}

How to download files in Chrome using Selenium Webdriver

//Get Chrome Driver
System.setProperty("webdriver.chrome.driver", "/path/to/chromedriver");
String downloadFilepath = "/path/to/download";

//Save Chrome Preferences in Hash Map
HashMap<String, Object> chromePrefs = new HashMap<String, Object>();
chromePrefs.put("profile.default_content_settings.popups", 0);
chromePrefs.put("download.default_directory", downloadFilepath);

//Save Chrome Opions
ChromeOptions options = new ChromeOptions();
HashMap<String, Object> chromeOptionsMap = new HashMap<String, Object>();
options.setExperimentalOptions("prefs", chromePrefs);
options.addArguments("--test-type");

//Set desired capability
DesiredCapabilities cap = DesiredCapabilities.chrome();
cap.setCapability(ChromeOptions.CAPABILITY, chromeOptionsMap);
cap.setCapability(CapabilityType.ACCEPT_SSL_CERTS, true);
cap.setCapability(ChromeOptions.CAPABILITY, options);

//Start Chrome Driver
WebDriver driver = new ChromeDriver(cap);