Declare a Firefox Driver

WebDriver driver = new FirefoxDriver();

How to handle Dialog box in Mozilla

If Browser("Browser").DialogExists Then    ----> to check whether dialog exist in Mozilla
    Browser("Browser").GetDialogText -----> to  get the text from Mozilla
    Browser("Browser").HandleDialog micOK    --->To click the ok button
    Browser("Browser").HandleDialog micCancel   -----> to click the cancel button
End If