I try to run
```python
        browser = Browser(self.marionette)
        browser.launch()

        browser.got_to_url('http://mozqa.com/data/firefox/layout/mozilla.html')
        browser.switch_to_content()

        browser.switch_to_chrome()
        browser.got_to_url('http://www.google.com/')
```
And it will fail, due to the URL will become `mozillahttp://www.google.com/` (first site's title + second site's url).
To prevent this problem, we can clear the url-bar before `send_keys`
```python
    def url(self, value):
        awesome_bar = self.marionette.find_element(*self._awesome_bar_locator)
        awesome_bar.clear()
        awesome_bar.send_keys(value)
```