TestNG Suite running for Multiple Test

I am trying to execute following testng Suite.

Below code is for testng.xml

<suite name="Suite" parallel="none">
   <test name="Module 1">
    <classes>
        <class name="com.testcases.Class1" />
    </classes>
  </test> 

  <test name="Module 2">
    <classes>
        <class name="com.testcases.Class2" />
    </classes>
  </test> 
</suite> 

Also, do have the class code snippets as shown below:

public class Class 1{
  @Test(dataProvider = "getdata")
    public void DoClass1(Hashtable<String, String> data){
       Some Code
    }
  @DataProvider
    public Object[][] getdata() {
      return TestUtil.getdata(Module, xls);
    }

  @AfterTest
    public void close()
    {
      driver.quit(); //Using to Close the FireFox
    }

Similarly I have the Code for Class2

Now When I run the Suite with following steps:

Class 1 - Open Browser Navigate

Class 2 - Open Browser Navigate

While running the suite Class 1 runs successfully and closes the FireFox Browser. For Class 2 - Prompts Unable to Open browser.

Please help what needs to be change / update.