Adding FirefoxDriver constructors that accept legacy XpiDriverService

Author: barancev

java/client/src/org/openqa/selenium/firefox/FirefoxDriver.java

@@ -124,10 +124,18 @@ public FirefoxDriver(GeckoDriverService service) {
     super(new DriverCommandExecutor(service), new FirefoxOptions());
   }
 
+  public FirefoxDriver(XpiDriverService service) {
+    super(new DriverCommandExecutor(service), new FirefoxOptions());
+  }
+
   public FirefoxDriver(GeckoDriverService service, FirefoxOptions options) {
     super(new DriverCommandExecutor(service), dropCapabilities(options));
   }
 
+  public FirefoxDriver(XpiDriverService service, FirefoxOptions options) {
+    super(new DriverCommandExecutor(service), dropCapabilities(options));
+  }
+
   private static CommandExecutor toExecutor(FirefoxOptions options) {
     Objects.requireNonNull(options, "No options to construct executor from");
     DriverService.Builder<?, ?> builder;