title: Modal dialog present Exception
body: <p>I try to click on <code>a</code> element, by this way:</p>
  
  <pre><code>WebElement title = driver.findElement(By.xpath("//a[text()=\"Delete this document library\"]"));
  title.click();
  </code></pre>
  
  <p>When I click on it manually, its opens a window:</p>
  
  <pre>The page at http://.. says
  Are you sure you want to delete the selected items?</pre>
  
  <p>with <code>OK</code> and <code>Cancel</code> buttons</p>
  
  <p>But when I run it with WebDriver (in <code>Firefox 20.0</code>), I get the next error:</p>
  
  <pre>[Exception]: Modal dialog present</pre>
  
  <p>and I don't see even the window.</p>
  
  <p>What can be the reason?</p>