http://chromedriver.storage.googleapis.com/index.html chromedriver的下载地址
http://selenium-release.storage.googleapis.com/index.html IEdriver的下载地址
https://github.com/mozilla/geckodriver/releases firefoxdriver的下载地址
问题积累：
1. 关于IE11不能定位的问题：解决方案：
For IE 11 only, you will need to set a registry entry on the target computer so that the driver can maintain a connection to the instance of Internet Explorer it creates. （这段告诉你需要修改注册表。）
For 32-bit Windows installations, the key you must examine in the registry editor is HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_BFCACHE. （32bit Windows看这里。）
For 64-bit Windows installations, the key is HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_BFCACHE. Please note that the FEATURE_BFCACHE subkey may or may not be present, and should be created if it is not present. Important: Inside this key, create a DWORD value named iexplore.exe with the value of 0.（64bit Windows看这里。）
翻译过来的意思即，修改你的注册表（Run->regedit->Enter），路径如下：
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\Main\FeatureControl\FEATURE_BFCACHE
如果FeatureControl下没有FEATURE_BFCACHE，就以FEATURE_BFCACHE为名new一个key！并在其下创建一个DWORD，取名为：iexplore.exe，value为0。
2. IE的click无效的解决方案：
使用模拟js点击：
((IJavaScriptExecutor)driver).ExecuteScript(“arguments[0].click();”, driver.FindElement(By.TagName(“button”)));
3. IE的sendkeys慢的解决方案：
IE的64位driver有bug，使用32位的driver
4. firefox中sendkeys报错的问题
firefox的版本问题，使用52版本的firefox可以解决
