Não consigo executar meu script em nenhum dos navegadores. Abaixo está o erro que recebo para o firefox. O local onde o firefox está instalado está correto. Não sei o que está errado.

Eu estou usando o Firefox 15. Selenium Java 2.2.0 e Eclipse Juno

Meu caso de teste é dado abaixo:

import static org.junit.Assert.*;
import org.junit.After; 
import org.junit.Before; 
import org.junit.Test; 
import org.openqa.selenium.By; 
import org.openqa.selenium.WebDriver; 
import org.openqa.selenium.firefox.FirefoxDriver;  
import org.openqa.selenium.firefox.FirefoxProfile;

public class FirstTest {
private WebDriver _driver;
@Before
 public void setUp() throws Exception {
System.setProperty("webdriver.firefox.driver","C:\\Program Files\\Mozilla Firefox15\\Firefox.exe");
FirefoxProfile firefoxProfile = new FirefoxProfile();
_driver = new FirefoxDriver(firefoxProfile);
}

@Test 
public void Login() throws Exception {
_driver.get("https://www.google.co.in/");
assertEquals("Google", _driver.getTitle());
_driver.findElement(By.id("lst-ib")).clear();
_driver.findElement(By.id("lst-ib")).sendKeys("selenium");
_driver.findElement(By.name("btnG")).click();
_driver.findElement(By.linkText("Selenium - Web Browser Automation")).click();
assertEquals(" ", _driver.getTitle());
assertEquals("Selenium - Web Browser Automation", _driver.getTitle());
}
@After public void tearDown() throws Exception {
_driver.quit();
}
}

Abaixo está o erro que recebo:

org.openqa.selenium.WebDriverException: Cannot find firefox binary in PATH. Make sure firefox is installed. OS appears to be: VISTA
Build info: version: '2.20.0', revision: '16008', time: '2012-02-27 19:03:59'
System info: os.name: 'Windows 7', os.arch: 'x86', os.version: '6.1', java.version: '1.6.0_26'
Driver info: driver.version: FirefoxDriver
    at org.openqa.selenium.firefox.internal.Executable.<init>(Executable.java:52)
    at org.openqa.selenium.firefox.FirefoxBinary.<init>(FirefoxBinary.java:56)
    at org.openqa.selenium.firefox.FirefoxBinary.<init>(FirefoxBinary.java:52)
    at org.openqa.selenium.firefox.FirefoxDriver.<init>(FirefoxDriver.java:88)
    at FirstTest.setUp(FirstTest.java:16)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:27)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:30)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

java.lang.NullPointerException
    at FirstTest.tearDown(FirstTest.java:31)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:36)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:68)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:47)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:300)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)