Yup..Installing browser plugins is possible with Selenium. With Chrome and Firefox, WebDriver supports the installation of extensions, remotely. Sample code is below for Chrome and Firefox:
For Chrome
File file = new File("extension.crx"); // zip files are also accepted
ChromeOptions options = new ChromeOptions();
options.addExtensions(file);
// Option 1: Locally.
WebDriver driver = new ChromeDriver(options);
// Option 2: Remotely
DesiredCapabilities capabilities = DesiredCapabilities.chrome();
capabilities.setCapability(ChromeOptions.CAPABILITY, options);
WebDriver driver = new RemoteWebDriver(new URL("http://localhost:4444/wd/hub"), capabilities);
For Firefox
File file = new File("extension.xpi");
FirefoxProfile firefoxProfile = new FirefoxProfile();
firefoxProfile.addExtension(file);
// Option 1: Locally
WebDriver driver = new FirefoxDriver(firefoxProfile);
// Option 2: Remotely
DesiredCapabilities capabilities = DesiredCapabilities.firefox();
capabilities.setCapability(FirefoxDriver.PROFILE, firefoxProfile);
WebDriver driver = new RemoteWebDriver(new URL("http://localhost:4444/wd/hub"), capabilities);