Chaining find_by_* seems to have no effect for xpath

Problem:

I want to find a `` from table, from given panel by using xpath and chaining find_by_* methods.
```

panel = browser.find_by_xpath('//*[@id="main"]//div[@class="heading"][contains(normalize-space(), "Table A")]/following-sibling::table')
panel.find_by_tag("td") # return two elements from Table A
panel.find_by_xpath('//td') # will return all of td's
```

The reason why I'm using the xpath is that I want to find a cell with value next to some "label cell": `//td[text()="Row 1"]/following-sibling::td[1]` and in my code I have many of such row's with same names.

Expected behavior: it will return only td's from given panel.

Xpaths were tested also on http://xpather.com/ and it's working like expected.

Splinter version: 0.21.0, selenium: selenium/standalone-firefox:4.27

Browser setup like this:
```
browser = Browser(
"remote",
command_executor=SELENIUM_URL,
)
```

Start by reproducing the chained find_by_xpath and find_by_tag calls from the issue with Splinter 0.21.0 and the stated Selenium setup. Trace the find_by_xpath entry point and compare descendant-scoped behavior with the leading // XPath; done means the XPath lookup returns only td elements from the selected panel while existing chaining behavior remains intact.

Written by the indexing model from the issue text.